| OAuth Working Group | M.B. Jones |
| Internet-Draft | Microsoft |
| Intended status: Standards Track | J. Bradley |
| Expires: January 13, 2014 | Ping Identity |
| N. Sakimura | |
| NRI | |
| July 12, 2013 |
JSON Web Token (JWT)
draft-ietf-oauth-json-web-token-09
JSON Web Token (JWT) is a compact URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JavaScript Object Notation (JSON) object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or MACed and/or encrypted.
The suggested pronunciation of JWT is the same as the English word "jot".
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JSON Web Token (JWT) is a compact claims representation format intended for space constrained environments such as HTTP Authorization headers and URI query parameters. JWTs encode claims to be transmitted as a JavaScript Object Notation (JSON) [RFC4627] object that is used as the payload of a JSON Web Signature (JWS) [JWS] structure or as the plaintext of a JSON Web Encryption (JWE) [JWE] structure, enabling the claims to be digitally signed or MACed and/or encrypted. JWTs are always represented using the JWS Compact Serialization or the JWE Compact Serialization.
The suggested pronunciation of JWT is the same as the English word "jot".
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in Key words for use in RFCs to Indicate Requirement Levels [RFC2119].
JWTs represent a set of claims as a JSON object that is encoded in a JWS and/or JWE structure. This JSON object is the JWT Claims Set. As per RFC 4627 [RFC4627] Section 2.2, the JSON object consists of zero or more name/value pairs (or members), where the names are strings and the values are arbitrary JSON values. These members are the claims represented by the JWT.
The member names within the JWT Claims Set are referred to as Claim Names. The corresponding values are referred to as Claim Values.
The contents of the JWT Header describe the cryptographic operations applied to the JWT Claims Set. If the JWT Header is a JWS Header, the JWT is represented as a JWS, and the claims are digitally signed or MACed, with the JWT Claims Set being the JWS Payload. If the JWT Header is a JWE Header, the JWT is represented as a JWE, and the claims are encrypted, with the JWT Claims Set being the input Plaintext. A JWT may be enclosed in another JWE or JWS structure to create a Nested JWT, enabling nested signing and encryption to be performed.
A JWT is represented as a sequence of URL-safe parts separated by period ('.') characters. Each part contains a base64url encoded value. The number of parts in the JWT is dependent upon the representation of the resulting JWS or JWE object using the JWS Compact Serialization or the JWE Compact Serialization.
The following example JWT Header declares that the encoded object is a JSON Web Token (JWT) and the JWT is MACed using the HMAC SHA-256 algorithm:
{"typ":"JWT",
"alg":"HS256"}
Base64url encoding the octets of the UTF-8 representation of the JWT Header yields this Encoded JWS Header value, which is used as the Encoded JWT Header:
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
The following is an example of a JWT Claims Set:
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
The following octet sequence, which is the UTF-8 representation of the JWT Claims Set above, is the JWS Payload:
[123, 34, 105, 115, 115, 34, 58, 34, 106, 111, 101, 34, 44, 13, 10, 32, 34, 101, 120, 112, 34, 58, 49, 51, 48, 48, 56, 49, 57, 51, 56, 48, 44, 13, 10, 32, 34, 104, 116, 116, 112, 58, 47, 47, 101, 120, 97, 109, 112, 108, 101, 46, 99, 111, 109, 47, 105, 115, 95, 114, 111, 111, 116, 34, 58, 116, 114, 117, 101, 125]
Base64url encoding the JWS Payload yields this Encoded JWS Payload (with line breaks for display purposes only):
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly 9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ
Signing the Encoded JWS Header and Encoded JWS Payload with the HMAC SHA-256 algorithm and base64url encoding the signature in the manner specified in [JWS], yields this Encoded JWS Signature:
dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk
Concatenating these parts in this order with period ('.') characters between the parts yields this complete JWT (with line breaks for display purposes only):
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9 . eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt cGxlLmNvbS9pc19yb290Ijp0cnVlfQ . dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk
This computation is illustrated in more detail in Appendix A.1 of [JWS]. See Appendix A for an example of an encrypted JWT.
The JWT Claims Set represents a JSON object whose members are the claims conveyed by the JWT. The Claim Names within a JWT Claims Set MUST be unique; receipients MUST either reject JWTs with duplicate Claim Names or use a JSON parser that returns only the lexically last duplicate member name, as specified in Section 15.12 (The JSON Object) of ECMAScript 5.1 [ECMAScript].
The set of claims that a JWT must contain to be considered valid is context-dependent and is outside the scope of this specification. Specific applications of JWTs will require implementations to understand and process some claims in particular ways. However, in the absence of such requirements, all claims that are not understood by implementations SHOULD be ignored.
There are three classes of JWT Claim Names: Reserved Claim Names, Public Claim Names, and Private Claim Names.
The following Claim Names are reserved. None of the claims defined below are intended to be mandatory to use, but rather, provide a starting point for a set of useful, interoperable claims. All the names are short because a core goal of JWTs is for the representation to be compact. Additional reserved Claim Names can be defined via the IANA JSON Web Token Claims registry Section 9.1.
The iss (issuer) claim identifies the principal that issued the JWT. The processing of this claim is generally application specific. The iss value is a case sensitive string containing a StringOrURI value. Use of this claim is OPTIONAL.
The sub (subject) claim identifies the principal that is the subject of the JWT. The Claims in a JWT are normally statements about the subject. The processing of this claim is generally application specific. The sub value is a case sensitive string containing a StringOrURI value. Use of this claim is OPTIONAL.
The aud (audience) claim identifies the audiences that the JWT is intended for. Each principal intended to process the JWT MUST identify itself with a value in audience claim. If the principal processing the claim does not identify itself with a value in the aud claim, then the JWT MUST be rejected. In the general case, the aud value is an array of case sensitive strings, each containing a StringOrURI value. In the special case when the JWT has one audience, the aud value MAY be a single case sensitive string containing a StringOrURI value. The interpretation of audience values is generally application specific. Use of this claim is OPTIONAL.
The exp (expiration time) claim identifies the expiration time on or after which the JWT MUST NOT be accepted for processing. The processing of the exp claim requires that the current date/time MUST be before the expiration date/time listed in the exp claim. Implementers MAY provide for some small leeway, usually no more than a few minutes, to account for clock skew. Its value MUST be a number containing an IntDate value. Use of this claim is OPTIONAL.
The nbf (not before) claim identifies the time before which the JWT MUST NOT be accepted for processing. The processing of the nbf claim requires that the current date/time MUST be after or equal to the not-before date/time listed in the nbf claim. Implementers MAY provide for some small leeway, usually no more than a few minutes, to account for clock skew. Its value MUST be a number containing an IntDate value. Use of this claim is OPTIONAL.
The iat (issued at) claim identifies the time at which the JWT was issued. This claim can be used to determine the age of the JWT. Its value MUST be a number containing an IntDate value. Use of this claim is OPTIONAL.
The jti (JWT ID) claim provides a unique identifier for the JWT. The identifier value MUST be assigned in a manner that ensures that there is a negligible probability that the same value will be accidentally assigned to a different data object. The jti claim can be used to prevent the JWT from being replayed. The jti value is a case sensitive string. Use of this claim is OPTIONAL.
The typ (type) claim MAY be used to declare a type for the contents of this JWT Claims Set in an application-specific manner in contexts where this is useful to the application. The typ value is a case sensitive string. Use of this claim is OPTIONAL.
The values used for the typ claim come from the same value space as the typ header parameter, with the same rules applying.
Claim Names can be defined at will by those using JWTs. However, in order to prevent collisions, any new Claim Name SHOULD either be registered in the IANA JSON Web Token Claims registry Section 9.1 or be a Public Name: a value that contains a Collision Resistant Namespace. In each case, the definer of the name or value needs to take reasonable precautions to make sure they are in control of the part of the namespace they use to define the Claim Name.
A producer and consumer of a JWT MAY agree to use Claim Names that are Private Names: names that are not Reserved Names Section 4.1 or Public Names Section 4.2. Unlike Public Names, Private Names are subject to collision and should be used with caution.
The members of the JSON object represented by the JWT Header describe the cryptographic operations applied to the JWT and optionally, additional properties of the JWT. The member names within the JWT Header are referred to as Header Parameter Names. These names MUST be unique; receipients MUST either reject JWTs with duplicate Header Parameter Names or use a JSON parser that returns only the lexically last duplicate member name, as specified in Section 15.12 (The JSON Object) of ECMAScript 5.1 [ECMAScript]. The corresponding values are referred to as Header Parameter Values.
JWS Header Parameters are defined by [JWS]. JWE Header Parameters are defined by [JWE]. This specification further specifies the use of the following header parameter in both the cases where the JWT is a JWS and where it is a JWE.
The typ (type) header parameter MAY be used to declare the type of this JWT in an application-specific manner in contexts where this is useful to the application. This parameter has no effect upon the JWT processing. If present, it is RECOMMENDED that its value be either JWT or urn:ietf:params:oauth:token-type:jwt to indicate that this object is a JWT. The typ value is a case sensitive string. Use of this header parameter is OPTIONAL.
The cty (content type) header parameter is used to declare structural information about the JWT. Its value MUST be a string.
In the normal case where nested signing or encryption operations are not employed, the use of this header parameter is NOT RECOMMENDED. In the case that nested signing or encryption is employed, the use of this header parameter is REQUIRED; in this case, the value MUST be JWT, to indicate that a Nested JWT is carried in this JWT.
The values used for the cty header parameter come from the same value space as the typ header parameter, with the same rules applying.
To support use cases where the JWT content is secured by a means other than a signature and/or encryption contained within the JWT (such as a signature on a data structure containing the JWT), JWTs MAY also be created without a signature or encryption. A plaintext JWT is a JWS using the none JWS alg header parameter value defined in JSON Web Algorithms (JWA) [JWA]; it is a JWS with the empty string for its JWS Signature value.
The following example JWT Header declares that the encoded object is a Plaintext JWT:
{"alg":"none"}
Base64url encoding the octets of the UTF-8 representation of the JWT Header yields this Encoded JWT Header:
eyJhbGciOiJub25lIn0
The following is an example of a JWT Claims Set:
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
Base64url encoding the octets of the UTF-8 representation of the JWT Claims Set yields this Encoded JWS Payload (with line breaks for display purposes only):
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
The Encoded JWS Signature is the empty string.
Concatenating these parts in this order with period ('.') characters between the parts yields this complete JWT (with line breaks for display purposes only):
eyJhbGciOiJub25lIn0 . eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt cGxlLmNvbS9pc19yb290Ijp0cnVlfQ .
To create a JWT, one MUST perform these steps. The order of the steps is not significant in cases where there are no dependencies between the inputs and outputs of the steps.
When validating a JWT the following steps MUST be taken. The order of the steps is not significant in cases where there are no dependencies between the inputs and outputs of the steps. If any of the listed steps fails then the JWT MUST be rejected for processing.
Processing a JWT inevitably requires comparing known strings to values in JSON objects. For example, in checking what the algorithm is, the Unicode string encoding alg will be checked against the member names in the JWT Header to see if there is a matching Header Parameter Name.
Comparisons between JSON strings and other Unicode strings MUST be performed by comparing Unicode code points without normalization as specified in the String Comparison Rules in Section 5.3 of [JWS].
JWTs use JSON Web Signature (JWS) [JWS] and JSON Web Encryption (JWE) [JWE] to sign and/or encrypt the contents of the JWT.
Of the JWA signing algorithms, only HMAC SHA-256 (HS256) and none MUST be implemented by conforming JWT implementations. It is RECOMMENDED that implementations also support RSASSA-PKCS1-V1_5 with the SHA-256 hash algorithm (RS256) and ECDSA using the P-256 curve and the SHA-256 hash algorithm (ES256). Support for other algorithms and key sizes is OPTIONAL.
If an implementation provides encryption capabilities, of the JWA encryption algorithms, only RSAES-PKCS1-V1_5 with 2048 bit keys (RSA1_5), AES Key Wrap with 128 and 256 bit keys (A128KW and A256KW), and the composite authenticated encryption algorithm using AES CBC and HMAC SHA-2 (A128CBC-HS256 and A256CBC-HS512) MUST be implemented by conforming implementations. It is RECOMMENDED that implementations also support using ECDH-ES to agree upon a key used to wrap the Content Encryption Key (ECDH-ES+A128KW and ECDH-ES+A256KW) and AES in Galois/Counter Mode (GCM) with 128 bit and 256 bit keys (A128GCM and A256GCM). Support for other algorithms and key sizes is OPTIONAL.
This specification establishes the IANA JSON Web Token Claims registry for reserved JWT Claim Names. The registry records the reserved Claim Name and a reference to the specification that defines it. This specification registers the Claim Names defined in Section 4.1.
Values are registered with a Specification Required [RFC5226] after a two-week review period on the [TBD]@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Expert(s) may approve registration once they are satisfied that such a specification will be published.
Registration requests must be sent to the [TBD]@ietf.org mailing list for review and comment, with an appropriate subject (e.g., "Request for access token type: example"). [[ Note to RFC-EDITOR: The name of the mailing list should be determined in consultation with the IESG and IANA. Suggested name: claims-reg-review. ]]
Within the review period, the Designated Expert(s) will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful.
IANA must only accept registry updates from the Designated Expert(s) and should direct all requests for registration to the review mailing list.
This specification registers the value token-type:jwt in the IANA urn:ietf:params:oauth registry established in An IETF URN Sub-Namespace for OAuth [RFC6755], which can be used to indicate that the content is a JWT.
This specification registers the JWT type value in the IANA JSON Web Signature and Encryption Type Values registry [JWS], which can be used to indicate that the content is a JWT.
This specification registers the application/jwt Media Type [RFC2046] in the MIME Media Type registry [RFC4288], which can be used to indicate that the content is a JWT.
All of the security issues faced by any cryptographic application must be faced by a JWT/JWS/JWE/JWK agent. Among these issues are protecting the user's private and symmetric keys, preventing various attacks, and helping the user avoid mistakes such as inadvertently encrypting a message for the wrong recipient. The entire list of security considerations is beyond the scope of this document.
All the security considerations in the JWS specification also apply to JWT, as do the JWE security considerations when encryption is employed. In particular, the JWS JSON Security Considerations and Unicode Comparison Security Considerations apply equally to the JWT Claims Set in the same manner that they do to the JWS Header.
While syntactically, the signing and encryption operations for Nested JWTs may be applied in any order, normally senders should sign the message and then encrypt the result (thus encrypting the signature). This prevents attacks in which the signature is stripped, leaving just an encrypted message, as well as providing privacy for the signer. Furthermore, signatures over encrypted text are not considered valid in many jurisdictions.
Note that potential concerns about security issues related to the order of signing and encryption operations are already addressed by the underlying JWS and JWE specifications; in particular, because JWE only supports the use of authenticated encryption algorithms, cryptographic concerns about the potential need to sign after encryption that apply in many contexts do not apply to this specification.
This example encrypts the same claims as used in Section 3.1 to the recipient using RSAES-PKCS1-V1_5 and AES_128_CBC_HMAC_SHA_256.
The following example JWE Header (with line breaks for display purposes only) declares that:
{"alg":"RSA1_5","enc":"A128CBC-HS256"}
Other than using the octets of the UTF-8 representation of the JWT Claims Set from Section 3.1 as the plaintext value, the computation of this JWT is identical to the computation of the JWE in Appendix A.2 of [JWE], including the keys used.
The final result in this example (with line breaks for display purposes only) is:
eyJhbGciOiJSU0ExXzUiLCJlbmMiOiJBMTI4Q0JDLUhTMjU2In0. QR1Owv2ug2WyPBnbQrRARTeEk9kDO2w8qDcjiHnSJflSdv1iNqhWXaKH4MqAkQtM oNfABIPJaZm0HaA415sv3aeuBWnD8J-Ui7Ah6cWafs3ZwwFKDFUUsWHSK-IPKxLG TkND09XyjORj_CHAgOPJ-Sd8ONQRnJvWn_hXV1BNMHzUjPyYwEsRhDhzjAD26ima sOTsgruobpYGoQcXUwFDn7moXPRfDE8-NoQX7N7ZYMmpUDkR-Cx9obNGwJQ3nM52 YCitxoQVPzjbl7WBuB7AohdBoZOdZ24WlN1lVIeh8v1K4krB8xgKvRU8kgFrEn_a 1rZgN5TiysnmzTROF869lQ. AxY8DCtDaGlsbGljb3RoZQ. MKOle7UQrG6nSxTLX6Mqwt0orbHvAKeWnDYvpIAeZ72deHxz3roJDXQyhxx0wKaM HDjUEOKIwrtkHthpqEanSBNYHZgmNOV7sln1Eu9g3J8. fiK51VwhsxJ-siBMR-YFiA
SAML 2.0 [OASIS.saml-core-2.0-os] provides a standard for creating security tokens with greater expressivity and more security options than supported by JWTs. However, the cost of this flexibility and expressiveness is both size and complexity. SAML's use of XML [W3C.CR-xml11-20021015] and XML DSIG [RFC3275] contributes to the size of SAML assertions; its use of XML and especially XML Canonicalization [W3C.REC-xml-c14n-20010315] contributes to their complexity.
JWTs are intended to provide a simple security token format that is small enough to fit into HTTP headers and query arguments in URIs. It does this by supporting a much simpler token model than SAML and using the JSON [RFC4627] object encoding syntax. It also supports securing tokens using Message Authentication Codes (MACs) and digital signatures using a smaller (and less flexible) format than XML DSIG.
Therefore, while JWTs can do some of the things SAML assertions do, JWTs are not intended as a full replacement for SAML assertions, but rather as a token format to be used when ease of implementation or compactness are considerations.
SAML Assertions are always statements made by an entity about a subject. JWTs are often used in the same manner, with the entity making the statements being represented by the iss (issuer) claim, and the subject being represented by the sub (subject) claim. However, with these claims being optional, other uses of the JWT format are also permitted.
Both JWTs and Simple Web Tokens SWT [SWT], at their core, enable sets of claims to be communicated between applications. For SWTs, both the claim names and claim values are strings. For JWTs, while claim names are strings, claim values can be any JSON type. Both token types offer cryptographic protection of their content: SWTs with HMAC SHA-256 and JWTs with a choice of algorithms, including signature, MAC, and encryption algorithms.
The authors acknowledge that the design of JWTs was intentionally influenced by the design and simplicity of Simple Web Tokens [SWT] and ideas for JSON tokens that Dick Hardt discussed within the OpenID community.
Solutions for signing JSON content were previously explored by Magic Signatures [MagicSignatures], JSON Simple Sign [JSS], and Canvas Applications [CanvasApp], all of which influenced this draft.
This specification is the work of the OAuth Working Group, which includes dozens of active and dedicated participants. In particular, the following individuals contributed ideas, feedback, and wording that influenced this specification:
Dirk Balfanz, Richard Barnes, Brian Campbell, Breno de Medeiros, Dick Hardt, Joe Hildebrand, Jeff Hodges, Edmund Jay, Yaron Y. Goland, Ben Laurie, James Manger, Prateek Mishra, Tony Nadalin, Axel Nennker, John Panzer, Emmanuel Raviart, David Recordon, Eric Rescorla, Jim Schaad, Paul Tarjan, Hannes Tschofenig, and Sean Turner.
Hannes Tschofenig and Derek Atkins chaired the OAuth working group and Sean Turner and Stephen Farrell served as Security area directors during the creation of this specification.
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