Access Tokens:

Access tokens are credentials needed to access protected resources. An access token is a data structure representing authorization permissions issued by the AS to the client. Access tokens are generated by the AS and consumed by the RS. The access token content is opaque to the client.

Access tokens can have different formats and various methods of utilization (e.g., cryptographic properties) based on the security requirements of the given deployment.

Introspection:

Introspection is a method for a resource server, or potentially a client, to query the authorization server for the active state and content of a received access token. This is particularly useful in those cases where the authorization decisions are very dynamic and/or where the received access token itself is an opaque reference, rather than a self-contained token. More information about introspection in OAuth 2.0 can be found in [RFC 7662].

Refresh Tokens:

Refresh tokens are credentials used to obtain access tokens. Refresh tokens are issued to the client by the authorization server and are used to obtain a new access token when the current access token expires or to obtain additional access tokens with identical or narrower scope (such access tokens may have a shorter lifetime and fewer permissions than authorized by the resource owner). Issuing a refresh token is optional at the discretion of the authorization server. If the authorization server issues a refresh token, it is included when issuing an access token (i.e., step (B) in Figure 1).

A refresh token in OAuth 2.0 is a string representing the authorization granted to the client by the resource owner. The string is usually opaque to the client. The token denotes an identifier used to retrieve the authorization information. Unlike access tokens, refresh tokens are intended for use only with authorization servers and are never sent to resource servers. In this framework, refresh tokens are encoded in binary instead of strings, if used.

Proof-of-Possession Tokens:

A token may be bound to a cryptographic key, which is then used to bind the token to a request authorized by the token. Such tokens are called proof-of-possession tokens (or PoP tokens).

The proof-of-possession security concept used here assumes that the AS acts as a trusted third party that binds keys to tokens. In the case of access tokens, these so-called PoP keys are then used by the client to demonstrate the possession of the secret to the RS when accessing the resource. The RS, when receiving an access token, needs to verify that the key used by the client matches the one bound to the access token. When this specification uses the term "access token", it is assumed to be a PoP access token unless specifically stated otherwise.

The key bound to the token (the PoP key) may use either symmetric or asymmetric cryptography. The appropriate choice of the kind of cryptography depends on the constraints of the IoT devices as well as on the security requirements of the use case.

Symmetric PoP key:

The AS generates a random, symmetric PoP key. The key is either stored to be returned on introspection calls or included in the token. Either the whole token or only the key MUST be encrypted in the latter case. The PoP key is also returned to client together with the token, protected by the secure channel.

Asymmetric PoP key:

An asymmetric key pair is generated by the client and the public key is sent to the AS (if it does not already have knowledge of the client's public key). Information about the public key, which is the PoP key in this case, is either stored to be returned on introspection calls or included inside the token and sent back to the client. The resource server consuming the token can identify the public key from the information in the token, which allows the client to use the corresponding private key for the proof of possession.

The token is either a simple reference or a structured information object (e.g., CWT [RFC 8392]) protected by a cryptographic wrapper (e.g., COSE [RFC 8152]). The choice of PoP key does not necessarily imply a specific credential type for the integrity protection of the token.

Scopes and Permissions:

In OAuth 2.0, the client specifies the type of permissions it is seeking to obtain (via the scope parameter) in the access token request. In turn, the AS may use the scope response parameter to inform the client of the scope of the access token issued. As the client could be a constrained device as well, this specification defines the use of CBOR encoding (see Section 5) for such requests and responses.

The values of the scope parameter in OAuth 2.0 are expressed as a list of space-delimited, case-sensitive strings with a semantic that is well known to the AS and the RS. More details about the concept of scopes are found under Section 3.3 of RFC 6749.

Claims:

Information carried in the access token or returned from introspection, called claims, is in the form of name-value pairs. An access token may, for example, include a claim identifying the AS that issued the token (via the iss claim) and what audience the access token is intended for (via the aud claim). The audience of an access token can be a specific resource, one resource, or many resource servers. The resource owner policies influence what claims are put into the access token by the authorization server.

While the structure and encoding of the access token varies throughout deployments, a standardized format has been defined with the JSON Web Token (JWT) [RFC 7519], where claims are encoded as a JSON object. In [RFC 8392], the CBOR Web Token (CWT) has been defined as an equivalent format using CBOR encoding.

Token and Introspection Endpoints:

The AS hosts the token endpoint that allows a client to request access tokens. The client makes a POST request to the token endpoint on the AS and receives the access token in the response (if the request was successful).

In some deployments, a token introspection endpoint is provided by the AS, which can be used by the RS and potentially the client, if they need to request additional information regarding a received access token. The requesting entity makes a POST request to the introspection endpoint on the AS and receives information about the access token in the response. (See "Introspection" above.)

+--------+                               +---------------+
|        |---(A)-- Token Request ------->|               |
|        |                               | Authorization |
|        |<--(B)-- Access Token ---------|    Server     |
|        |    + Access Information       |               |
|        |    + Refresh Token (optional) +---------------+
|        |                                      ^ |
|        |            Introspection Request  (D)| |
| Client |                         Response     | |(E)
|        |            (optional exchange)       | |
|        |                                      | v
|        |                               +--------------+
|        |---(C)-- Token + Request ----->|              |
|        |                               |   Resource   |
|        |<--(F)-- Protected Resource ---|    Server    |
|        |                               |              |
+--------+                               +--------------+
  

Requesting an Access Token (A):

The client makes an access token request to the token endpoint at the AS. This framework assumes the use of PoP access tokens (see Section 3.1 for a short description) wherein the AS binds a key to an access token. The client may include permissions it seeks to obtain and information about the credentials it wants to use for proof of possession (e.g., symmetric/asymmetric cryptography or a reference to a specific key) of the access token.

Access Token Response (B):

If the request from the client has been successfully verified, authenticated, and authorized, the AS returns an access token and optionally a refresh token. Note that only certain grant types support refresh tokens. The AS can also return additional parameters, referred to as "Access Information". In addition to the response parameters defined by OAuth 2.0 and the PoP access token extension, this framework defines parameters that can be used to inform the client about capabilities of the RS, e.g., the profile the RS supports. More information about these parameters can be found in Section 5.8.4.

Resource Request (C):

The client interacts with the RS to request access to the protected resource and provides the access token. The protocol to use between the client and the RS is not restricted to CoAP. HTTP, HTTP/2 [RFC 9113], QUIC [RFC 9000], MQTT [MQTT5.0], Bluetooth Low Energy [BLE], etc., are also viable candidates.

Depending on the device limitations and the selected protocol, this exchange may be split up into two parts:

(1)

the client sends the access token containing, or referencing, the authorization information to the RS that will be used for subsequent resource requests by the client, and

(2)

the client makes the resource access request using the communication security protocol and other Access Information obtained from the AS.

The client and the RS mutually authenticate using the security protocol specified in the profile (see step (B)) and the keys obtained in the access token or the Access Information. The RS verifies that the token is integrity protected and originated by the AS. It then compares the claims contained in the access token with the resource request. If the RS is online, validation can be handed over to the AS using token introspection (see messages (D) and (E)) over HTTP or CoAP.

Token Introspection Request (D):

A resource server may be configured to introspect the access token by including it in a request to the introspection endpoint at that AS. Token introspection over CoAP is defined in Section 5.9 and for HTTP in [RFC 7662].

Note that token introspection is an optional step and can be omitted if the token is self-contained and the resource server is prepared to perform the token validation on its own.

Token Introspection Response (E):

The AS validates the token and returns the most recent parameters, such as scope, audience, validity, etc., associated with it back to the RS. The RS then uses the received parameters to process the request to either accept or to deny it.

Protected Resource (F):

If the request from the client is authorized, the RS fulfills the request and returns a response with the appropriate response code. The RS uses the dynamically established keys to protect the response according to the communication security protocol used.

Credential Provisioning

In constrained environments, it cannot be assumed that the client and the RS are part of a common key infrastructure. Therefore, the AS provisions credentials and associated information to allow mutual authentication between the client and the RS. The resulting security association between the client and the RS may then also be used to bind these credentials to the access tokens the client uses.

Proof of Possession

The ACE framework, by default, implements proof of possession for access tokens, i.e., that the token holder can prove being a holder of the key bound to the token. The binding is provided by the cnf (confirmation) claim [RFC 8747], indicating what key is used for proof of possession. If a client needs to submit a new access token, e.g., to obtain additional access rights, they can request that the AS binds this token to the same key as the previous one.

ACE Profiles

The client or RS may be limited in the encodings or protocols it supports. To support a variety of different deployment settings, specific interactions between the client and RS are defined in an ACE profile. In the ACE framework, the AS is expected to manage the matching of compatible profile choices between a client and an RS. The AS informs the client of the selected profile using the ace_profile parameter in the token response.

• The request has been received on an unsecured channel.
• The RS has no valid access token for the sender of the request regarding the requested action on that resource.
• The RS has a valid access token for the sender of the request, but that token does not authorize the requested action on the requested resource.

• An audience element contains an identifier the client should request at the AS, as suggested by the RS. With this parameter, when included in the access token request to the AS, the AS is able to restrict the use of the access token to specific RSs. See Section 6.9 for a discussion of this parameter.
• A kid (key identifier) element contains the key identifier of a key used in an existing security association between the client and the RS. The RS expects the client to request an access token bound to this key in order to avoid having to reestablish the security association.
• A cnonce element contains a client-nonce. See Section 5.3.1.
• A scope element contains the suggested scope that the client should request towards the AS.

    4.01 Unauthorized
    Content-Format: application/ace+cbor
    Payload :
    {
     / AS / 1 : "coaps://as.example.com/token",
     / audience / 5 : "coaps://rs.example.com",
     / scope / 9 : "rTempC",
     / cnonce / 39 : h'e0a156bb3f'
    }

a4                                   # map(4)
   01                                # unsigned(1) (=AS)
   78 1c                             # text(28)
      636f6170733a2f2f61732e657861
      6d706c652e636f6d2f746f6b656e   # "coaps://as.example.com/token"
   05                                # unsigned(5) (=audience)
   76                                # text(22)
      636f6170733a2f2f72732e657861
      6d706c652e636f6d               # "coaps://rs.example.com"
   09                                # unsigned(9) (=scope)
   66                                # text(6)
      7254656d7043                   # "rTempC"
   18 27                             # unsigned(39) (=cnonce)
   45                                # bytes(5)
      e0a156bb3f                     #

• An RS sending a cnonce parameter in an AS Request Creation Hints message MUST store information to validate that a given cnonce is fresh. How this is implemented internally is out of scope for this specification. Expiration of client-nonces should be based roughly on the time it would take a client to obtain an access token after receiving the AS Request Creation Hints, with some allowance for unexpected delays.
• A client receiving a cnonce parameter in an AS Request Creation Hints message MUST include this in the parameters when requesting an access token at the AS, using the cnonce parameter from Section 5.8.4.4.
• If an AS grants an access token request containing a cnonce parameter, it MUST include this value in the access token, using the cnonce claim specified in Section 5.10.
• An RS that is using the client-nonce mechanism and that receives an access token MUST verify that this token contains a cnonce claim, with a client-nonce value that is fresh according to the information stored at the first step above. If the cnonce claim is not present or if the cnonce claim value is not fresh, the RS MUST discard the access token. If this was an interaction with the authz-info endpoint, the RS MUST also respond with an error message using a response code equivalent to the CoAP code 4.01 (Unauthorized).

• The grant_type parameter is OPTIONAL in the context of this framework (as opposed to REQUIRED in [RFC 6749]). If that parameter is missing, the default value "client_credentials" is implied.
• The audience parameter from [RFC 8693] is OPTIONAL to request an access token bound to a specific audience.
• The cnonce parameter defined in Section 5.8.4.4 is REQUIRED if the RS provided a client-nonce in the AS Request Creation Hints message (Section 5.3).
• The scope parameter MAY be encoded as a byte string instead of the string encoding specified in Section 3.3 of RFC 6749 or in order to allow compact encoding of complex scopes. The syntax of such a binary encoding is explicitly not specified here and left to profiles or applications. Note specifically that a binary encoded scope does not necessarily use the space character '0x20' to delimit scope-tokens.
• The client can send an empty (null value) ace_profile parameter to indicate that it wants the AS to include the ace_profile parameter in the response. See Section 5.8.4.3.
• A client MUST be able to use the parameters from [RFC 9201] in an access token request to the token endpoint, and the AS MUST be able to process these additional parameters.

Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: application/ace+cbor
Payload:
{
  / client_id / 24 : "myclient",
  / audience /  5  : "tempSensor4711"
}

Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
OSCORE: 0x09, 0x05, 0x44, 0x6C
  (h=0, k=1, n=001, partialIV= 0x05, kid=[0x44, 0x6C])
Content-Format: application/oscore
Payload:
  0x44025d1/ ... (full payload omitted for brevity) ... /68b3825e

Decrypted payload:
{
  / client_id / 24 : "myclient",
  / req_cnf / 4 : {
    / COSE_Key / 1 : {
      / kty /  1 : 2 / EC2 /,
      / kid /  2 : h'11',
      / crv / -1 : 1 / P-256 /,
      / x /   -2 : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
      / y /   -3 : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
    }
  }
}

Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: application/ace+cbor
Payload:
{
  / client_id / 24 : "myclient",
  / audience /   5 : "valve424",
  / scope /      9 : "read",
  / req_cnf /    4 : {
     / kid /        3 : b64'6kg0dXJM13U'
  }
}

ace_profile:

This parameter is OPTIONAL unless the request included an empty ace_profile parameter, in which case it is MANDATORY. This indicates the profile that the client MUST use towards the RS. See Section 5.8.4.3 for the formatting of this parameter. If this parameter is absent, the AS assumes that the client implicitly knows which profile to use towards the RS.

token_type:

This parameter is OPTIONAL, as opposed to REQUIRED in [RFC 6749]. By default, implementations of this framework SHOULD assume that the token_type is "PoP". If a specific use case requires another token_type (e.g., "Bearer") to be used, then this parameter is REQUIRED.

Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Payload:
{
  / access_token / 1 : b64'SlAV32hk'/ ...
   (remainder of CWT omitted for brevity;
   CWT contains COSE_Key in the cnf claim)/,
  / ace_profile / 38 : "coap_dtls",
  / expires_in /   2 : 3600,
  / cnf / 8 : {
    / COSE_Key / 1 : {
      / kty / 1 : 4 / Symmetric /,
      / kid / 2 : b64'39Gqlw',
      / k /  -1 : b64'hJtXhkV8FJG+Onbc6mxC'
    }
  }
}

• When using CoAP, the payload MUST be encoded as a CBOR map, with the Content-Format "application/ace+cbor". When using HTTP, the payload is encoded in JSON, as specified in Section 5.2 of RFC 6749.
• A response code equivalent to the CoAP code 4.00 (Bad Request) MUST be used for all error responses, except for invalid_client, where a response code equivalent to the CoAP code 4.01 (Unauthorized) MAY be used under the same conditions as specified in Section 5.2 of RFC 6749.
• The parameters error, error_description, and error_uri MUST be abbreviated using the codes specified in Table 5, when a CBOR encoding is used.
• The error code (i.e., value of the error parameter) MUST be abbreviated, as specified in Table 3, when a CBOR encoding is used.

• If the client submits an asymmetric key in the token request that the RS cannot process, the AS MUST reject that request with a response code equivalent to the CoAP code 4.00 (Bad Request), including the error code "unsupported_pop_key" specified in Table 3.
• If the client and the RS it has requested an access token for do not share a common profile, the AS MUST reject that request with a response code equivalent to the CoAP code 4.00 (Bad Request), including the error code "incompatible_ace_profiles" specified in Table 3.

ace_profile

This parameter is OPTIONAL. This indicates the profile that the RS MUST use with the client. See Section 5.8.4.3 for more details on the formatting of this parameter. If this parameter is absent, the AS assumes that the RS implicitly knows which profile to use towards the client.

cnonce

This parameter is OPTIONAL. This is a client-nonce provided to the AS by the client. The RS MUST verify that this corresponds to the client-nonce previously provided to the client in the AS Request Creation Hints. See Sections [5.3] and [5.8.4.4]. Its value is a byte string when encoded in CBOR and is the base64url encoding of this byte string without padding when encoded in JSON [RFC 4648].

cti

This parameter is OPTIONAL. This is the cti claim associated to this access token. This parameter has the same meaning and processing rules as the jti parameter defined in Section 3.1.2 of RFC 7662 except that its value is a byte string when encoded in CBOR and is the base64url encoding of this byte string without padding when encoded in JSON [RFC 4648].

exi

This parameter is OPTIONAL. This is the expires_in claim associated to this access token. See Section 5.10.3.

Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Payload:
{
  / active /      10 : true,
  / scope /        9 : "read",
  / ace_profile / 38 : 1 / coap_dtls /,
  / cnf /          8 : {
    / COSE_Key / 1 : {
      / kty / 1 : 4 / Symmetric /,
      / kid / 2 : b64'39Gqlw',
      / k /  -1 : b64'hJtXhkV8FJG+Onbc6mxC'
    }
  }
}

• If content is sent and CoAP is used, the payload MUST be encoded as a CBOR map and the Content-Format "application/ace+cbor" MUST be used. For HTTP, the encoding defined in Section 2.3 of RFC 6749 is used.
• If the credentials used by the requesting entity (usually the RS) are invalid, the AS MUST respond with the response code equivalent to the CoAP code 4.01 (Unauthorized) and use the required and optional parameters from Section 2.3 of RFC 7662.
• If the requesting entity does not have the right to perform this introspection request, the AS MUST respond with a response code equivalent to the CoAP code 4.03 (Forbidden). In this case, no payload is returned.
• The parameters error, error_description, and error_uri MUST be abbreviated using the codes specified in Table 5.
• The error codes MUST be abbreviated using the codes specified in the registry defined by Section 8.4.

• If the verification of the security wrapper fails, or the token was issued by an AS that does not have the right to issue tokens for the receiving RS, the RS MUST discard the token and, if this was an interaction with authz-info, return an error message with a response code equivalent to the CoAP code 4.01 (Unauthorized).
• If the claims cannot be obtained, the RS MUST discard the token and, in case of an interaction via the authz-info endpoint, return an error message with a response code equivalent to the CoAP code 4.00 (Bad Request).

iss

The iss claim (if present) must identify the AS that has produced the security protection for the access token. If that is not the case, the RS MUST discard the token. If this was an interaction with authz-info, the RS MUST also respond with a response code equivalent to the CoAP code 4.01 (Unauthorized).

exp

The expiration date must be in the future. If that is not the case, the RS MUST discard the token. If this was an interaction with authz-info, the RS MUST also respond with a response code equivalent to the CoAP code 4.01 (Unauthorized). Note that the RS has to terminate access rights to the protected resources at the time when the tokens expire.

aud

The aud claim must refer to an audience that the RS identifies with. If that is not the case, the RS MUST discard the token. If this was an interaction with authz-info, the RS MUST also respond with a response code equivalent to the CoAP code 4.03 (Forbidden).

scope

The RS must recognize value of the scope claim. If that is not the case, the RS MUST discard the token. If this was an interaction with authz-info, the RS MUST also respond with a response code equivalent to the CoAP code 4.00 (Bad Request). The RS MAY provide additional information in the error response to clarify what went wrong.

• The token is a CWT and includes an exp claim and possibly the nbf claim. The RS verifies these by comparing them to values from its internal clock, as defined in [RFC 7519]. In this case, the RS's internal clock must reflect the current date and time or at least be synchronized with the AS's clock. How this clock synchronization would be performed is out of scope for this specification.
• The RS verifies the validity of the token by performing an introspection request, as specified in Section 5.9. This requires the RS to have a reliable network connection to the AS and to be able to handle two secure sessions in parallel (C to RS and RS to AS).
• In order to support token expiration for devices that have no reliable way of synchronizing their internal clocks, this specification defines the following approach: The claim exi (expires in) can be used to provide the RS with the lifetime of the token in seconds from the time the RS first receives the token. This mechanism only works for self-contained tokens, i.e., CWTs and JWTs. For CWTs, this parameter is encoded as an unsigned integer, while JWTs encode this as JSON number.
• Processing this claim requires that the RS does the following:
  • For each token the RS receives that contains an exi claim, keep track of the time it received that token and revisit that list regularly to expunge expired tokens.
  • Keep track of the identifiers of tokens containing the exi claim that have expired (in order to avoid accepting them again). In order to avoid an unbounded memory usage growth, this MUST be implemented in the following way when the exi claim is used:
    • When creating the token, the AS MUST add a cti claim (or jti for JWTs) to the access token. The value of this claim MUST be created as the binary representation of the concatenation of the identifier of the RS with a sequence number counting the tokens containing an exi claim, issued by this AS for the RS.
    • The RS MUST store the highest sequence number of an expired token containing the exi claim that it has seen and treat tokens with lower sequence numbers as expired. Note that this could lead to discarding valid tokens with lower sequence numbers if the AS where to issue tokens of different validity time for the same RS. The assumption is that typically tokens in such a scenario would all have the same validity time.

• The client knows a default validity time for all tokens it is using (i.e., how long a token is valid after being issued). This information could be provisioned to the client when it is registered at the AS or published by the AS in a way that the client can query.
• The AS informs the client about the token validity using the expires_in parameter in the Access Information.

C-AS

All communication between the client and the authorization server MUST be encrypted and integrity and replay protected. Furthermore, responses from the AS to the client MUST be bound to the client's request to avoid attacks where the attacker swaps the intended response for an older one valid for a previous request. This requires that the client and the authorization server have previously exchanged either a shared secret or their public keys in order to negotiate a secure communication. Furthermore, the client MUST be able to determine whether an AS has the authority to issue access tokens for a certain RS. This can, for example, be done through preconfigured lists or through an online lookup mechanism that in turn also must be secured.

RS-AS

The communication between the resource server and the authorization server via the introspection endpoint MUST be encrypted and integrity and replay protected. Furthermore, responses from the AS to the RS MUST be bound to the RS's request. This requires that the RS and the authorization server have previously exchanged either a shared secret or their public keys in order to negotiate a secure communication. Furthermore, the RS MUST be able to determine whether an AS has the authority to issue access tokens itself. This is usually configured out of band but could also be performed through an online lookup mechanism, provided that it is also secured in the same way.

C-RS

The initial communication between the client and the resource server cannot be secured in general, since the RS is not in possession of on access token for that client, which would carry the necessary parameters. If both parties support DTLS without client authentication, it is RECOMMENDED to use this mechanism for protecting the initial communication. After the client has successfully transmitted the access token to the RS, a secure communication protocol MUST be established between the client and RS for the actual resource request. This protocol MUST provide confidentiality, integrity, and replay protection, as well as a binding between requests and responses. This requires that the client learned either the RS's public key or received a symmetric proof-of-possession key bound to the access token from the AS. The RS must have learned either the client's public key, a shared symmetric key from the claims in the token, or an introspection request. Since ACE does not provide profile negotiation between the C and RS, the client MUST have learned what profile the RS supports (e.g., from the AS or preconfigured) and initiated the communication accordingly.

• A malicious client may hold back tokens with the exi claim in order to prolong their lifespan.
• If an RS loses state (e.g., due to an unscheduled reboot), it may lose the current values of counters tracking the exi claims of tokens it is storing.

Name:

The name of the parameter.

CBOR Key:

CBOR map key for the parameter. Different ranges of values use different registration policies [RFC 8126]. Integer values from -256 to 255 are designated as Standards Action. Integer values from -65536 to -257 and from 256 to 65535 are designated as Specification Required. Integer values greater than 65535 are designated as Expert Review. Integer values less than -65536 are marked as Private Use.

Value Type:

The CBOR data types allowable for the values of this parameter.

Reference:

This contains a pointer to the public specification of the Request Creation Hint abbreviation, if one exists.

Value:

ace.ai

Description:

ACE-OAuth authz-info endpoint resource.

Reference:

RFC 9200

Name:

unsupported_pop_key

Usage Location:

token error response

Protocol Extension:

RFC 9200

Change Controller:

IETF

Reference:

Section 5.8.3 of RFC 9200

Name:

incompatible_ace_profiles

Usage Location:

token error response

Protocol Extension:

RFC 9200

Change Controller:

IETF

Reference:

Section 5.8.3 of RFC 9200

Name:

The OAuth Error Code name, refers to the name in Section 5.2 of RFC 6749, e.g., "invalid_request".

CBOR Value:

CBOR abbreviation for this error code. Integer values less than -65536 are marked as Private Use; all other values use the registration policy Expert Review [RFC 8126].

Reference:

This contains a pointer to the public specification of the error code abbreviation, if one exists.

Original Specification:

This contains a pointer to the public specification of the error code, if one exists.

Name:

The name of the grant type, as specified in Section 1.3 of RFC 6749.

CBOR Value:

CBOR abbreviation for this grant type. Integer values less than -65536 are marked as Private Use; all other values use the registration policy Expert Review [RFC 8126].

Reference:

This contains a pointer to the public specification of the grant type abbreviation, if one exists.

Original Specification:

This contains a pointer to the public specification of the grant type, if one exists.

Name:

PoP

Additional Token Endpoint Response Parameters:

cnf, rs_cnf (see Section 3.1 of RFC 8747 and Section 3.2 of RFC 9201).

HTTP Authentication Scheme(s):

N/A

Change Controller:

IETF

Reference:

RFC 9200

Name:

The name of the token type, as registered in the "OAuth Access Token Types" registry, e.g., "Bearer".

CBOR Value:

CBOR abbreviation for this token type. Integer values less than -65536 are marked as Private Use; all other values use the registration policy Expert Review [RFC 8126].

Reference:

This contains a pointer to the public specification of the OAuth token type abbreviation, if one exists.

Original Specification:

This contains a pointer to the public specification of the OAuth token type, if one exists.

Name:

Bearer

CBOR Value:

1

Reference:

RFC 9200

Original Specification:

[RFC 6749]

Name:

PoP

CBOR Value:

2

Reference:

RFC 9200

Original Specification:

RFC 9200

Name:

The name of the profile to be used as the value of the profile attribute.

Description:

Text giving an overview of the profile and the context it is developed for.

CBOR Value:

CBOR abbreviation for this profile name. Different ranges of values use different registration policies [RFC 8126]. Integer values from -256 to 255 are designated as Standards Action. Integer values from -65536 to -257 and from 256 to 65535 are designated as Specification Required. Integer values greater than 65535 are designated as Expert Review. Integer values less than -65536 are marked as Private Use.

Reference:

This contains a pointer to the public specification of the profile abbreviation, if one exists.

Name:

ace_profile

Parameter Usage Location:

token response

Change Controller:

IETF

Reference:

Sections [5.8.2] and [5.8.4.3] of RFC 9200

Name:

The OAuth Parameter name, refers to the name in the OAuth parameter registry, e.g., client_id.

CBOR Key:

CBOR map key for this parameter. Integer values less than -65536 are marked as Private Use; all other values use the registration policy Expert Review [RFC 8126].

Value Type:

The allowable CBOR data types for values of this parameter.

Reference:

This contains a pointer to the public specification of the OAuth parameter abbreviation, if one exists.

Original Specification

This contains a pointer to the public specification of the OAuth parameter, if one exists.

Name:

ace_profile

Description:

The ACE profile used between the client and RS.

Change Controller:

IETF

Reference:

Section 5.9.2 of RFC 9200

Name:

cnonce

Description:

"client-nonce". A nonce previously provided to the AS by the RS via the client. Used to verify token freshness when the RS cannot synchronize its clock with the AS.

Change Controller:

IETF

Reference:

Section 5.9.2 of RFC 9200

Name

cti

Description

"CWT ID". The identifier of a CWT as defined in [RFC 8392].

Change Controller

IETF

Reference

Section 5.9.2 of RFC 9200

Name:

exi

Description:

"Expires in". Lifetime of the token in seconds from the time the RS first sees it. Used to implement a weaker form of token expiration for devices that cannot synchronize their internal clocks.

Change Controller:

IETF

Reference:

Section 5.9.2 of RFC 9200

Name:

The OAuth Parameter name, refers to the name in the OAuth parameter registry, e.g., client_id.

CBOR Key:

CBOR map key for this parameter. Integer values less than -65536 are marked as Private Use; all other values use the registration policy Expert Review [RFC 8126].

Value Type:

The allowable CBOR data types for values of this parameter.

Reference:

This contains a pointer to the public specification of the introspection response parameter abbreviation, if one exists.

Original Specification

This contains a pointer to the public specification of the OAuth Token Introspection parameter, if one exists.

Claim Name:

ace_profile

Claim Description:

The ACE profile a token is supposed to be used with.

Change Controller:

IETF

Reference:

Section 5.10 of RFC 9200

Claim Name:

cnonce

Claim Description:

"client-nonce". A nonce previously provided to the AS by the RS via the client. Used to verify token freshness when the RS cannot synchronize its clock with the AS.

Change Controller:

IETF

Reference:

Section 5.10 of RFC 9200

Claim Name:

exi

Claim Description:

"Expires in". Lifetime of the token in seconds from the time the RS first sees it. Used to implement a weaker form of token expiration for devices that cannot synchronize their internal clocks.

Change Controller:

IETF

Reference:

Section 5.10.3 of RFC 9200

Claim Name:

ace_profile

Claim Description:

The ACE profile a token is supposed to be used with.

JWT Claim Name:

ace_profile

Claim Key:

38

Claim Value Type:

integer

Change Controller:

IETF

Reference:

Section 5.10 of RFC 9200

Claim Name:

cnonce

Claim Description:

The client-nonce sent to the AS by the RS via the client.

JWT Claim Name:

cnonce

Claim Key:

39

Claim Value Type:

byte string

Change Controller:

IETF

Reference:

Section 5.10 of RFC 9200

Claim Name:

exi

Claim Description:

The expiration time of a token measured from when it was received at the RS in seconds.

JWT Claim Name:

exi

Claim Key:

40

Claim Value Type:

unsigned integer

Change Controller:

IETF

Reference:

Section 5.10.3 of RFC 9200

Claim Name:

scope

Claim Description:

The scope of an access token, as defined in [RFC 6749].

JWT Claim Name:

scope

Claim Key:

9

Claim Value Type:

byte string or text string

Change Controller:

IETF

Reference:

Section 4.2 of RFC 8693

Type name:

application

Subtype name:

ace+cbor

Required parameters:

N/A

Optional parameters:

N/A

Encoding considerations:

Must be encoded as a CBOR map containing the protocol parameters defined in RFC 9200.

Security considerations:

See Section 6 of RFC 9200

Interoperability considerations:

N/A

Published specification:

RFC 9200

Applications that use this media type:

The type is used by authorization servers, clients, and resource servers that support the ACE framework with CBOR encoding, as specified in RFC 9200.

Fragment identifier considerations:

N/A

Additional information:

N/A

Person & email address to contact for further information:

IESG <iesg@ietf.org>

Intended usage:

COMMON

Restrictions on usage:

none

Author:

Ludwig Seitz <ludwig.seitz@combitech.se>

Change controller:

IETF

Media Type:

application/ace+cbor

Encoding:

-

ID:

19

Reference:

RFC 9200

• Point squatting should be discouraged. Reviewers are encouraged to get sufficient information for registration requests to ensure that the usage is not going to duplicate one that is already registered and that the point is likely to be used in deployments. The zones tagged as Private Use are intended for testing purposes and closed environments; code points in other ranges should not be assigned for testing.
• Specifications are needed for the first-come, first-serve range if they are expected to be used outside of closed environments in an interoperable way. When specifications are not provided, the description provided needs to have sufficient information to identify what the point is being used for.
• Experts should take into account the expected usage of fields when approving point assignment. The fact that there is a range for Standards Track documents does not mean that a Standards Track document cannot have points assigned outside of that range. The length of the encoded value should be weighed against how many code points of that length are left, i.e., the size of device it will be used on.
• Since a high degree of overlap is expected between these registries and the contents of the OAuth parameters [IANA.OAuthParameters] registries, experts should require new registrations to maintain alignment with parameters from OAuth that have comparable functionality. Deviation from this alignment should only be allowed if there are functional differences that are motivated by the use case and that cannot be easily or efficiently addressed by comparable OAuth parameters.

[IANA.CborWebTokenClaims]

IANA, "CBOR Web Token (CWT) Claims",
<https://www.iana.org/assignments/cwt>.

[IANA.CoreParameters]

IANA, "Constrained RESTful Environments (CoRE) Parameters",
<https://www.iana.org/assignments/core-parameters>.

[IANA.JsonWebTokenClaims]

IANA, "JSON Web Token Claims",
<https://www.iana.org/assignments/jwt>.

[IANA.OAuthAccessTokenTypes]

IANA, "OAuth Access Token Types",
<https://www.iana.org/assignments/oauth-parameters>.

[IANA.OAuthExtensionsErrorRegistry]

IANA, "OAuth Extensions Error Registry",
<https://www.iana.org/assignments/oauth-parameters>.

[IANA.OAuthParameters]

IANA, "OAuth Parameters",
<https://www.iana.org/assignments/oauth-parameters>.

[IANA.TokenIntrospectionResponse]

IANA, "OAuth Token Introspection Response",
<https://www.iana.org/assignments/oauth-parameters>.

[RFC2119]

S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3986]

T. Berners-Lee, R. Fielding, and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.

[RFC4648]

S. Josefsson, "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.

[RFC6347]

E. Rescorla, and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012,
<https://www.rfc-editor.org/info/rfc6347>.

[RFC6749]

D. Hardt, "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.

[RFC6750]

M. Jones, and D. Hardt, "The OAuth 2.0 Authorization Framework: Bearer Token Usage", RFC 6750, DOI 10.17487/RFC6750, October 2012,
<https://www.rfc-editor.org/info/rfc6750>.

[RFC6838]

N. Freed, J. Klensin, and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.

[RFC6920]

S. Farrell, D. Kutscher, C. Dannewitz, B. Ohlman, A. Keranen, and P. Hallam-Baker, "Naming Things with Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013,
<https://www.rfc-editor.org/info/rfc6920>.

[RFC7252]

Z. Shelby, K. Hartke, and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.

[RFC7519]

M. Jones, J. Bradley, and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.

[RFC7662]

J. Richer, "OAuth 2.0 Token Introspection", RFC 7662, DOI 10.17487/RFC7662, October 2015,
<https://www.rfc-editor.org/info/rfc7662>.

[RFC8126]

M. Cotton, B. Leiba, and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[RFC8152]

J. Schaad, "CBOR Object Signing and Encryption (COSE)", RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.

[RFC8174]

B. Leiba, "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017,
<https://www.rfc-editor.org/info/rfc8174>.

[RFC8392]

M. Jones, E. Wahlstroem, S. Erdtman, and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, May 2018,
<https://www.rfc-editor.org/info/rfc8392>.

[RFC8610]

H. Birkholz, C. Vigano, and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, June 2019,
<https://www.rfc-editor.org/info/rfc8610>.

[RFC8693]

M. Jones, A. Nadalin, B. Campbell, J. Bradley, and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693, DOI 10.17487/RFC8693, January 2020,
<https://www.rfc-editor.org/info/rfc8693>.

[RFC8747]

M. Jones, L. Seitz, G. Selander, S. Erdtman, and H. Tschofenig, "Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March 2020,
<https://www.rfc-editor.org/info/rfc8747>.

[RFC8949]

C. Bormann, and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.

[RFC9201]

L Seitz, "Additional OAuth Parameters for Authentication and Authorization in Constrained Environments (ACE)", RFC 9201, DOI 10.17487/RFC9201, August 2022,
<https://www.rfc-editor.org/info/rfc9201>.

[BLE]

Bluetooth Special Interest Group, "Core Specification 5.3", Section 4.4, July 2021,
<https://www.bluetooth.com/specifications/bluetooth-core-specification/>.

[DCAF]

S. Gerdes, O. Bergmann, and C. Bormann, "Delegated CoAP Authentication and Authorization Framework (DCAF)", Internet-Draft draft-gerdes-ace-dcaf-authorize-04, October 2015,
<https://datatracker.ietf.org/doc/html/draft-gerdes-ace-dcaf-authorize-04>.

[Margi10impact]

C. Margi, B. de Oliveira, G. de Sousa, M. Simplicio Jr, P. Barreto, T. Carvalho, M. Naeslund, and R. Gold, "Impact of Operating Systems on Wireless Sensor Networks (Security) Applications and Testbeds", DOI 10.1109/ICCCN.2010.5560028, August 2010,
<https://doi.org/10.1109/ICCCN.2010.5560028>.

[MQTT5.0]

A. Banks, E. Briggs, K. Borgendale, and R. Gupta, "MQTT Version 5.0", March 2019,
<https://docs.oasis-open.org/mqtt/mqtt/v5.0/mqtt-v5.0.html>.

[OAUTH-RPCC]

RISE SICS AB, L. Seitz, S. Erdtman, and M. Tiloca, "Raw-Public-Key and Pre-Shared-Key as OAuth client credentials", Internet-Draft draft-erdtman-oauth-rpcc-00, November 2017,
<https://datatracker.ietf.org/doc/html/draft-erdtman-oauth-rpcc-00>.

[POP-KEY-DIST]

GITDA, J. Bradley, P. Hunt, M. Jones, H. Tschofenig, and M. Meszaros, "OAuth 2.0 Proof-of-Possession: Authorization Server to Client Key Distribution", Internet-Draft draft-ietf-oauth-pop-key-distribution-07, March 2019,
<https://datatracker.ietf.org/doc/html/draft-ietf-oauth-pop-key-distribution-07>.

[RFC4949]

R. Shirey, "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.

[RFC6690]

Z. Shelby, "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.

[RFC6819]

T. Lodderstedt, M. McGloin, and P. Hunt, "OAuth 2.0 Threat Model and Security Considerations", RFC 6819, DOI 10.17487/RFC6819, January 2013,
<https://www.rfc-editor.org/info/rfc6819>.

[RFC7009]

T. Lodderstedt, S. Dronia, and M. Scurtescu, "OAuth 2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009, August 2013,
<https://www.rfc-editor.org/info/rfc7009>.

[RFC7228]

C. Bormann, M. Ersue, and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.

[RFC7521]

B. Campbell, C. Mortimore, M. Jones, and Y. Goland, "Assertion Framework for OAuth 2.0 Client Authentication and Authorization Grants", RFC 7521, DOI 10.17487/RFC7521, May 2015,
<https://www.rfc-editor.org/info/rfc7521>.

[RFC7591]

J. Richer, M. Jones, J. Bradley, M. Machulak, and P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol", RFC 7591, DOI 10.17487/RFC7591, July 2015,
<https://www.rfc-editor.org/info/rfc7591>.

[RFC7641]

K. Hartke, "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.

[RFC7744]

L. Seitz, S. Gerdes, G. Selander, M. Mani, and S. Kumar, "Use Cases for Authentication and Authorization in Constrained Environments", RFC 7744, DOI 10.17487/RFC7744, January 2016,
<https://www.rfc-editor.org/info/rfc7744>.

[RFC7959]

C. Bormann, and Z. Shelby, "Block-Wise Transfers in the Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>.

[RFC8252]

W. Denniss, and J. Bradley, "OAuth 2.0 for Native Apps", BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017,
<https://www.rfc-editor.org/info/rfc8252>.

[RFC8259]

T. Bray, "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.

[RFC8414]

M. Jones, N. Sakimura, and J. Bradley, "OAuth 2.0 Authorization Server Metadata", RFC 8414, DOI 10.17487/RFC8414, June 2018,
<https://www.rfc-editor.org/info/rfc8414>.

[RFC8446]

E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.

[RFC8516]

A. Keranen, ""Too Many Requests" Response Code for the Constrained Application Protocol", RFC 8516, DOI 10.17487/RFC8516, January 2019,
<https://www.rfc-editor.org/info/rfc8516>.

[RFC8613]

G. Selander, J. Mattsson, F. Palombini, and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.

[RFC8628]

W. Denniss, J. Bradley, M. Jones, and H. Tschofenig, "OAuth 2.0 Device Authorization Grant", RFC 8628, DOI 10.17487/RFC8628, August 2019,
<https://www.rfc-editor.org/info/rfc8628>.

[RFC9000]

J. Iyengar, and M. Thomson, "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.

[RFC9110]

R. Fielding, M. Nottingham, and J. Reschke, "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.

[RFC9113]

M. Thomson, and C. Benfield, "HTTP/2", RFC 9113, DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/info/rfc9113>.

[RFC9147]

E. Rescorla, H. Tschofenig, and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.

[RFC9202]

S Gerdes, O Bergmann, C Bormann, G Selander, and L Seitz, "Datagram Transport Layer Security (DTLS) Profile for Authentication and Authorization for Constrained Environments (ACE)", RFC 9202, DOI 10.17487/RFC9202, August 2022,
<https://www.rfc-editor.org/info/rfc9202>.

[RFC9203]

F Palombini, L Seitz, G Selander, and M Gunnarsson, "The Object Security for Constrained RESTful Environments (OSCORE) Profile of the Authentication and Authorization for Constrained Environments (ACE) Framework", RFC 9203, DOI 10.17487/RFC9203, August 2022,
<https://www.rfc-editor.org/info/rfc9203>.

Low Power Radio:

Many IoT devices are equipped with a small battery that needs to last for a long time. For many constrained wireless devices, the highest energy cost is associated to transmitting or receiving messages (roughly by a factor of 10 compared to AES) [Margi10impact]. It is therefore important to keep the total communication overhead low, including minimizing the number and size of messages sent and received, which has an impact of choice on the message format and protocol. By using CoAP over UDP and CBOR-encoded messages, some of these aspects are addressed. Security protocols contribute to the communication overhead and can, in some cases, be optimized. For example, authentication and key establishment may, in certain cases where security requirements allow, be replaced by the provisioning of security context by a trusted third party, using transport or application-layer security.

Low CPU Speed:

Some IoT devices are equipped with processors that are significantly slower than those found in most current devices on the Internet. This typically has implications on what timely cryptographic operations a device is capable of performing, which in turn impacts, e.g., protocol latency. Symmetric key cryptography may be used instead of the computationally more expensive public key cryptography where the security requirements so allow, but this may also require support for trusted, third-party-assisted secret key establishment using transport- or application-layer security.

Small Amount of Memory:

Microcontrollers embedded in IoT devices are often equipped with only a small amount of RAM and flash memory, which places limitations on what kind of processing can be performed and how much code can be put on those devices. To reduce code size, fewer and smaller protocol implementations can be put on the firmware of such a device. In this case, CoAP may be used instead of HTTP, symmetric-key cryptography may be used instead of public-key cryptography, and CBOR may be used instead of JSON. An authentication and key establishment protocol, e.g., the DTLS handshake, in comparison with assisted key establishment, also has an impact on memory and code footprints.

User Interface Limitations:

Protecting access to resources is both an important security as well as privacy feature. End users and enterprise customers may not want to give access to the data collected by their IoT device or to functions it may offer to third parties. Since the classical approach of requesting permissions from end users via a rich user interface does not work in many IoT deployment scenarios, these functions need to be delegated to user-controlled devices that are better suitable for such tasks, such as smartphones and tablets.

Communication Constraints:

In certain constrained settings, an IoT device may not be able to communicate with a given device at all times. Devices may be sleeping or just disconnected from the Internet because of general lack of connectivity in the area, cost reasons, or security reasons, e.g., to avoid an entry point for denial-of-service attacks.

The communication interactions this framework builds upon (as shown graphically in Figure 1) may be accomplished using a variety of different protocols, and not all parts of the message flow are used in all applications due to the communication constraints. Deployments making use of CoAP are expected, but this framework is not limited to them. Other protocols, such as HTTP or Bluetooth Smart communication, that do not necessarily use IP could also be used. The latter raises the need for application-layer security over the various interfaces.

CBOR, COSE, CWT:

When using this framework, it is RECOMMENDED to use CBOR [RFC 8949] as the data format. Where CBOR data needs to be protected, the use of COSE [RFC 8152] is RECOMMENDED. Furthermore, where self-contained tokens are needed, it is RECOMMENDED to use CWT [RFC 8392]. These measures aim at reducing the size of messages sent over the wire, the RAM size of data objects that need to be kept in memory, and the size of libraries that devices need to support.

CoAP:

When using this framework, it is RECOMMENDED to use CoAP [RFC 7252] instead of HTTP. This does not preclude the use of other protocols specifically aimed at constrained devices, e.g., Bluetooth Low Energy (see Section 3.2). This aims again at reducing the size of messages sent over the wire, the RAM size of data objects that need to be kept in memory, and the size of libraries that devices need to support.

Access Information:

This framework defines the name "Access Information" for data concerning the RS that the AS returns to the client in an access token response (see Section 5.8.2). This aims at enabling scenarios where a powerful client supporting multiple profiles needs to interact with an RS for which it does not know the supported profiles and the raw public key.

Proof of Possession:

This framework makes use of proof-of-possession tokens, using the cnf claim [RFC 8747]. A request parameter cnf and a Response parameter cnf, both having a value space semantically and syntactically identical to the cnf claim, are defined for the token endpoint to allow requesting and stating confirmation keys. This aims at making token theft harder. Token theft is specifically relevant in constrained use cases, as communication often passes through middleboxes, which could be able to steal bearer tokens and use them to gain unauthorized access.

Authz-Info endpoint:

This framework introduces a new way of providing access tokens to an RS by exposing an authz-info endpoint to which access tokens can be POSTed. This aims at reducing the size of the request message and the code complexity at the RS. The size of the request message is problematic, since many constrained protocols have severe message size limitations at the physical layer (e.g., in the order of 100 bytes). This means that larger packets get fragmented, which in turn combines badly with the high rate of packet loss and the need to retransmit the whole message if one packet gets lost. Thus, separating sending of the request and sending of the access tokens helps to reduce fragmentation.

Client Credentials Grant:

In this framework, the use of the client credentials grant is RECOMMENDED for machine-to-machine communication use cases, where manual intervention of the resource owner to produce a grant token is not feasible. The intention is that the resource owner would instead prearrange authorization with the AS based on the client's own credentials. The client can then (without manual intervention) obtain access tokens from the AS.

Introspection:

In this framework, the use of access token introspection is RECOMMENDED in cases where the client is constrained in a way that it cannot easily obtain new access tokens (i.e., it has connectivity issues that prevent it from communicating with the AS). In that case, it is RECOMMENDED to use a long-term token that could be a simple reference. The RS is assumed to be able to communicate with the AS and can therefore perform introspection in order to learn the claims associated with the token reference. The advantage of such an approach is that the resource owner can change the claims associated to the token reference without having to be in contact with the client, thus granting or revoking access rights.

Resource Owner

• Make sure that the RS is registered at the AS. This includes making known to the AS which profiles, token_type, scopes, and key types (symmetric/asymmetric) the RS supports. Also making it known to the AS which audience(s) the RS identifies itself with.
• Make sure that clients can discover the AS that is in charge of the RS.
• If the client-credentials grant is used, make sure that the AS has the necessary, up-to-date access control policies for the RS.

Requesting Party

• Make sure that the client is provisioned the necessary credentials to authenticate to the AS.
• Make sure that the client is configured to follow the security requirements of the requesting party when issuing requests (e.g., minimum communication security requirements or trust anchors).
• Register the client at the AS. This includes making known to the AS which profiles, token_types, and key types (symmetric/asymmetric) for the client.

Authorization Server

• Register the RS and manage corresponding security contexts.
• Register clients and authentication credentials.
• Allow resource owners to configure and update access control policies related to their registered RSs.
• Expose the token endpoint to allow clients to request tokens.
• Authenticate clients that wish to request a token.
• Process a token request using the authorization policies configured for the RS.
• Optionally, expose the introspection endpoint that allows RSs to submit token introspection requests.
• If providing an introspection endpoint, authenticate RSs that wish to get an introspection response.
• If providing an introspection endpoint, process token introspection requests.
• Optionally, handle token revocation.
• Optionally, provide discovery metadata. See [RFC 8414].
• Optionally, handle refresh tokens.

Client

• Discover the AS in charge of the RS that is to be targeted with a request.
• Submit the token request (see step (A) of Figure 1).
  • Authenticate to the AS.
  • Optionally (if not preconfigured), specify which RS, which resource(s), and which action(s) the request(s) will target.
  • If raw public keys (RPKs) or certificates are used, make sure the AS has the right RPK or certificate for this client.
• Process the access token and Access Information (see step (B) of Figure 1).
  • Check that the Access Information provides the necessary security parameters (e.g., PoP key or information on communication security protocols supported by the RS).
  • Safely store the proof-of-possession key.
  • If provided by the AS, safely store the refresh token.
• Send the token and request to the RS (see step (C) of Figure 1).
  • Authenticate towards the RS (this could coincide with the proof-of-possession process).
  • Transmit the token as specified by the AS (default is to the authz-info endpoint; alternative options are specified by profiles).
  • Perform the proof-of-possession procedure as specified by the profile in use (this may already have been taken care of through the authentication procedure).
• Process the RS response (see step (F) of Figure 1) of the RS.

Resource Server

• Expose a way to submit access tokens. By default, this is the authz-info endpoint.
• Process an access token.
  • Verify the token is from a recognized AS.
  • Check the token's integrity.
  • Verify that the token applies to this RS.
  • Check that the token has not expired (if the token provides expiration information).
  • Store the token so that it can be retrieved in the context of a matching request.
  Note: The order proposed here is not normative; any process that arrives at an equivalent result can be used. A noteworthy consideration is whether one can use cheap operations early on to quickly discard nonapplicable or invalid tokens before performing expensive cryptographic operations (e.g., doing an expiration check before verifying a signature).
• Process a request.
  • Set up communication security with the client.
  • Authenticate the client.
  • Match the client against existing tokens.
  • Check that tokens belonging to the client actually authorize the requested action.
  • Optionally, check that the matching tokens are still valid, using introspection (if this is possible.)
• Send a response following the agreed upon communication security mechanism(s).
• Safely store credentials, such as raw public keys, for authentication or proof-of-possession keys linked to access tokens.

• Optionally, define new methods for the client to discover the necessary permissions and AS for accessing a resource different from the one proposed in Sections [5.1] and [4]
• Optionally, specify new grant types (Section 5.4).
• Optionally, define the use of client certificates as client credential type (Section 5.5).
• Specify the communication protocol the client and RS must use (e.g., CoAP) (Sections [5] and [5.8.4.3]).
• Specify the security protocol the client and RS must use to protect their communication (e.g., OSCORE or DTLS). This must provide encryption and integrity and replay protection (Section 5.8.4.3).
• Specify how the client and the RS mutually authenticate (Section 4).
• Specify the proof-of-possession protocol(s) and how to select one if several are available. Also specify which key types (e.g., symmetric/asymmetric) are supported by a specific proof-of-possession protocol (Section 5.8.4.2).
• Specify a unique ace_profile identifier (Section 5.8.4.3).
• If introspection is supported, specify the communication and security protocol for introspection (Section 5.9).
• Specify the communication and security protocol for interactions between the client and AS. This must provide encryption, integrity protection, replay protection, and a binding between requests and responses (Sections [5] and [5.8]).
• Specify how/if the authz-info endpoint is protected, including how error responses are protected (Section 5.10.1).
• Optionally, define other methods of token transport than the authz-info endpoint (Section 5.10.1).

• The identifier of the client or RS.
• The profiles that the client or RS supports.
• The scopes that the RS supports.
• The audiences that the RS identifies with.
• The key types (e.g., pre-shared symmetric key, raw public key, key length, and other key parameters) that the client or RS supports.
• The types of access tokens the RS supports (e.g., CWT).
• If the RS supports CWTs, the COSE parameters for the crypto wrapper (e.g., algorithm, key-wrap algorithm, and key-length) that the RS supports.
• The expiration time for access tokens issued to this RS (unless the RS accepts a default time chosen by the AS).
• The symmetric key shared between the client and AS (if any).
• The symmetric key shared between the RS and AS (if any).
• The raw public key of the client or RS (if any).
• Whether the RS has synchronized time (and thus is able to use the exp claim) or not.

Use of TLS

OAuth 2.0 requires the use of TLS to protect the communication between the AS and client when requesting an access token, between the client and RS when accessing a resource, and between the AS and RS if introspection is used. This framework requires similar security properties but does not require that they be realized with TLS. See Section 5.

Cardinality of grant_type parameter

In client-to-AS requests using OAuth 2.0, the grant_type parameter is required (per [RFC 6749]). In this framework, this parameter is optional. See Section 5.8.1.

Encoding of scope parameter

In client-to-AS requests using OAuth 2.0, the scope parameter is string encoded (per [RFC 6749]). In this framework, this parameter may also be encoded as a byte string. See Section 5.8.1.

Cardinality of token_type parameter

In AS-to-client responses using OAuth 2.0, the token_type parameter is required (per [RFC 6749]). In this framework, this parameter is optional. See Section 5.8.2.

Access token retention

In OAuth 2.0, the access token may be sent with every request to the RS. The exact use of access tokens depends on the semantics of the application and the session management concept it uses. In this framework, the RS must be able to store these tokens for later use. See Section 5.10.1.

A:

The client first generates a public-private key pair used for communication security with the RS.

The client sends a CoAP POST request to the token endpoint at the AS. The security of this request can be transport or application layer. It is up the communication security profile to define. In the example, it is assumed that both the client and AS have performed mutual authentication, e.g., via DTLS. The request contains the public key of the client and the audience parameter set to "tempSensorInLivingRoom", a value that the temperature sensor identifies itself with. The AS evaluates the request and authorizes the client to access the resource.

B:

The AS responds with a 2.05 (Content) response containing the Access Information, including the access token. The PoP access token contains the public key of the client, and the Access Information contains the public key of the RS. For communication security, this example uses DTLS RawPublicKey between the client and the RS. The issued token will have a short validity time, i.e., exp close to iat, in order to mitigate attacks using stolen client credentials. The token includes claims, such as scope, with the authorized access that an owner of the temperature device can enjoy. In this example, the scope claim issued by the AS informs the RS that the owner of the token that can prove the possession of a key is authorized to make a GET request against the /temperature resource and a POST request on the /firmware resource. Note that the syntax and semantics of the scope claim are application specific.

Note: In this example, it is assumed that the client knows what resource it wants to access and is therefore able to request specific audience and scope claims for the access token.

         Authorization
  Client    Server
    |         |
    |<=======>| DTLS Connection Establishment
    |         |   and mutual authentication
    |         |
A:  +-------->| Header: POST (Code=0.02)
    |  POST   | Uri-Path:"token"
    |         | Content-Format: application/ace+cbor
    |         | Payload: <Request-Payload>
    |         |
B:  |<--------+ Header: 2.05 Content
    |  2.05   | Content-Format: application/ace+cbor
    |         | Payload: <Response-Payload>
    |         |
        

Request-Payload :
{
  / audience / 5 : "tempSensorInLivingRoom",
  / client_id / 24 : "myclient",
  / req_cnf / 4 : {
  / COSE_Key / 1 : {
      / kid / 2 : b64'1Bg8vub9tLe1gHMzV76e',
      / kty / 1 : 2 / EC2 /,
      / crv / -1 : 1 / P-256 /,
      / x / -2 : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU',
      / y / -3 : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0'
    }
  }
}

Response-Payload :
{
  / access_token / 1 : b64'0INDoQEKoQVNKkXfb7xaWqMT'/ .../,
  / rs_cnf / 41 : {
    / COSE_Key / 1 : {
      / kid / 2 : b64'c29tZSBwdWJsaWMga2V5IGlk',
      / kty / 1 : 2 / EC2 /,
      / crv / -1 : 1 / P-256 /,
      / x / -2   : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
      / y / -3   : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
    }
  }
}

{
  / aud / 3 : "tempSensorInLivingRoom",
  / iat / 6 : 1563451500,
  / exp / 4 : 1563453000,
  / scope / 9 :  "temperature_g firmware_p",
  / cnf / 8 : {
    / COSE_Key / 1 : {
      / kid / 2 : b64'1Bg8vub9tLe1gHMzV76e',
      / kty / 1 : 2 / EC2 /,
      / crv / -1 : 1 / P-256 /,
      / x / -2 : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU',
      / y / -3 : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0'
    }
  }
}

C:

The client then sends the PoP access token to the authz-info endpoint at the RS. This is a plain CoAP POST request, i.e., no transport or application-layer security is used between the client and RS since the token is integrity protected between the AS and RS. The RS verifies that the PoP access token was created by a known and trusted AS, which it applies to this RS, and that it is valid. The RS caches the security context together with authorization information about this client contained in the PoP access token.

           Resource
 Client     Server
    |         |
C:  +-------->| Header: POST (Code=0.02)
    |  POST   | Uri-Path:"authz-info"
    |         | Payload: 0INDoQEKoQVN ...
    |         |
    |<--------+ Header: 2.04 Changed
    |  2.04   |
    |         |

F:

The RS responds over the same DTLS channel with a CoAP 2.05 Content response containing a resource representation as payload.

           Resource
 Client     Server
    |         |
    |<=======>| DTLS Connection Establishment
    |         |   using Raw Public Keys
    |         |
    +-------->| Header: GET (Code=0.01)
    | GET     | Uri-Path: "temperature"
    |         |
    |         |
    |         |
F:  |<--------+ Header: 2.05 Content
    | 2.05    | Payload: <sensor value>
    |         |
      

A:

The client sends a CoAP POST request to the token endpoint at the AS. The request contains the audience parameter set to "PACS1337" (Physical Access System (PACS)), a value that identifies the physical access control system to which the individual doors are connected. The AS generates an access token as an opaque string, which it can match to the specific client and the targeted audience. It furthermore generates a symmetric proof-of-possession key. The communication security and authentication between the client and AS is assumed to have been provided at the transport layer (e.g., via DTLS) using a pre-shared security context (pre-shared key (PSK), RPK, or certificate).

B:

The AS responds with a CoAP 2.05 Content response, containing as payload the Access Information, including the access token and the symmetric proof-of-possession key. Communication security between the C and RS will be DTLS and PreSharedKey. The PoP key is used as the PreSharedKey.

         Authorization
 Client     Server
    |         |
    |<=======>| DTLS Connection Establishment
    |         |   and mutual authentication
    |         |
A:  +-------->| Header: POST (Code=0.02)
    |  POST   | Uri-Path:"token"
    |         | Content-Format: application/ace+cbor
    |         | Payload: <Request-Payload>
    |         |
B:  |<--------+ Header: 2.05 Content
    |         | Content-Format: application/ace+cbor
    |  2.05   | Payload: <Response-Payload>
    |         |
    

Request-Payload:
{
  / client_id / 24 : "keyfob",
  / audience / 5   : "PACS1337"
}

Response-Payload:
{
  / access_token / 1 : b64'VGVzdCB0b2tlbg',
  / cnf / 8 : {
    / COSE_Key / 1 : {
      / kid / 2 : b64'c29tZSBwdWJsaWMga2V5IGlk',
      / kty / 1 : 4 / Symmetric /,
      / k / -1  : b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE'
    }
  }
}

C:

Next, the client POSTs the access token to the authz-info endpoint in the RS. This is a plain CoAP request, i.e., no DTLS between the client and RS. Since the token is an opaque string, the RS cannot verify it on its own, and thus defers to respond to the client with a status code until after step E.

D:

The RS sends the token to the introspection endpoint on the AS using a CoAP POST request. In this example, the RS and AS are assumed to have performed mutual authentication using a pre-shared security context (PSK, RPK, or certificate) with the RS acting as the DTLS client.

E:

The AS provides the introspection response (2.05 Content) containing parameters about the token. This includes the confirmation key (cnf) parameter that allows the RS to verify the client's proof of possession in step F. Note that our example in Figure 19 assumes a preestablished key (e.g., one used by the client and the RS for a previous token) that is now only referenced by its key identifier kid.

After receiving message E, the RS responds to the client's POST in step C with the CoAP response code 2.01 (Created).

           Resource
  Client    Server
    |         |
C:  +-------->| Header: POST (T=CON, Code=0.02)
    |  POST   | Uri-Path:"authz-info"
    |         | Payload: b64'VGVzdCB0b2tlbg'
    |         |
    |         |     Authorization
    |         |       Server
    |         |          |
    |      D: +--------->| Header: POST (Code=0.02)
    |         |  POST    | Uri-Path: "introspect"
    |         |          | Content-Format: application/ace+cbor
    |         |          | Payload: <Request-Payload>
    |         |          |
    |      E: |<---------+ Header: 2.05 Content
    |         |  2.05    | Content-Format: application/ace+cbor
    |         |          | Payload: <Response-Payload>
    |         |          |
    |         |
    |<--------+ Header: 2.01 Created
    |  2.01   |
    |         |

Request-Payload:
{
  / token /     11 : b64'VGVzdCB0b2tlbg',
  / client_id / 24 : "FrontDoor"
}

Response-Payload:
{
  / active / 10 : true,
  / aud /     3 : "lockOfDoor4711",
  / scope /   9 : "open close",
  / iat /     6 : 1563454000,
  / cnf /     8 : {
         / kid / 3 : b64'c29tZSBwdWJsaWMga2V5IGlk'
  }
}

F:

The RS responds with an appropriate response over the secure DTLS channel.

           Resource
  Client    Server
    |         |
    |<=======>| DTLS Connection Establishment
    |         |   using Pre Shared Key
    |         |
    +-------->| Header: PUT (Code=0.03)
    | PUT     | Uri-Path: "state"
    |         | Payload: <new state for the lock>
    |         |
F:  |<--------+ Header: 2.04 Changed
    | 2.04    | Payload: <new state for the lock>
    |         |
            

Ludwig Seitz

Göran Selander

Erik Wahlstroem

Samuel Erdtman

Hannes Tschofenig