jwt-0.4.0: JSON Web Token (JWT) decoding and encoding

MaintainerStefan Saasen <stefan@saasen.me>
Safe HaskellNone




This implementation of JWT is based on http://self-issued.info/docs/draft-ietf-oauth-json-web-token.html (Version 16) but currently only implements the minimum required to work with the Atlassian Connect framework.

Known limitations:

  • Only HMAC SHA-256 algorithm is currently a supported signature algorithm
  • There is currently no verification of time related information (exp, nbf, iat).
  • Registered claims are not validated


Encoding & Decoding JWTs


There are three use cases supported by the set of decoding/verification functions:

  1. Plaintext JWTs (http://tools.ietf.org/html/draft-ietf-oauth-json-web-token-16#section-6). This is supported by the decode function decode. As a client you don't care about signing or encrypting so you only get back a JWT UnverifiedJWT. I.e. the type makes it clear that no signature verification was attempted.
  2. Signed JWTs you want to verify using a known secret. This is what decodeAndVerifySignature supports, given a secret and JSON it will return a JWT VerifiedJWT if the signature can be verified.
  3. Signed JWTs that need to be verified using a secret that depends on information contained in the JWT. E.g. the secret depends on some claim, therefore the JWT needs to be decoded first and after retrieving the appropriate secret value, verified in a subsequent step. This is supported by using the verify function which given a JWT UnverifiedJWT and a secret will return a JWT VerifiedJWT iff the signature can be verified.

decode :: JSON -> Maybe (JWT UnverifiedJWT)Source

Decode a claims set without verifying the signature. This is useful if information from the claim set is required in order to verify the claim (e.g. the secret needs to be retrieved based on unverified information from the claims set).

>>> :{
     input = "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzb21lIjoicGF5bG9hZCJ9.Joh1R2dYzkRvDkqv3sygm5YyK8Gi4ShZqbhK2gxcs2U" :: T.Text
     mJwt = decode input
 in fmap header mJwt
Just (JWTHeader {typ = Just "JWT", cty = Nothing, alg = Just HS256})


>>> :{
     input = "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzb21lIjoicGF5bG9hZCJ9.Joh1R2dYzkRvDkqv3sygm5YyK8Gi4ShZqbhK2gxcs2U" :: T.Text
     mJwt = decode input
 in fmap claims mJwt
Just (JWTClaimsSet {iss = Nothing, sub = Nothing, aud = Nothing, exp = Nothing, nbf = Nothing, iat = Nothing, jti = Nothing, unregisteredClaims = fromList [("some",String "payload")]})

verify :: Secret -> JWT UnverifiedJWT -> Maybe (JWT VerifiedJWT)Source

Using a known secret and a decoded claims set verify that the signature is correct and return a verified JWT token as a result.

This will return a VerifiedJWT if and only if the signature can be verified using the given secret.

The separation between decode and verify is very useful if you are communicating with multiple different services with different secrets and it allows you to lookup the correct secret for the unverified JWT before trying to verify it. If this is not an isuse for you (there will only ever be one secret) then you should just use decodeAndVerifySignature.

>>> :{
     input = "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzb21lIjoicGF5bG9hZCJ9.Joh1R2dYzkRvDkqv3sygm5YyK8Gi4ShZqbhK2gxcs2U" :: T.Text
     mUnverifiedJwt = decode input
     mVerifiedJwt = verify (secret "secret") =<< mUnverifiedJwt
 in signature =<< mVerifiedJwt
Just (Signature "Joh1R2dYzkRvDkqv3sygm5YyK8Gi4ShZqbhK2gxcs2U")

decodeAndVerifySignature :: Secret -> JSON -> Maybe (JWT VerifiedJWT)Source

Decode a claims set and verify that the signature matches by using the supplied secret. The algorithm is based on the supplied header value.

This will return a VerifiedJWT if and only if the signature can be verified using the given secret.

>>> :{
     input = "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzb21lIjoicGF5bG9hZCJ9.Joh1R2dYzkRvDkqv3sygm5YyK8Gi4ShZqbhK2gxcs2U" :: T.Text
     mJwt = decodeAndVerifySignature (secret "secret") input
 in signature =<< mJwt
Just (Signature "Joh1R2dYzkRvDkqv3sygm5YyK8Gi4ShZqbhK2gxcs2U")


encodeSigned :: Algorithm -> Secret -> JWTClaimsSet -> JSONSource

Encode a claims set using the given secret

>>> :{
     cs = def { -- def returns a default JWTClaimsSet
        iss = stringOrURI "Foo"
      , unregisteredClaims = Map.fromList [("http://example.com/is_root", (Bool True))]
     key = secret "secret-key"
 in encodeSigned HS256 key cs

encodeUnsigned :: JWTClaimsSet -> JSONSource

Encode a claims set without signing it

>>> :{
     cs = def { -- def returns a default JWTClaimsSet
     iss = stringOrURI "Foo"
   , iat = intDate 1394700934
   , unregisteredClaims = Map.fromList [("http://example.com/is_root", (Bool True))]
 in encodeUnsigned cs

Utility functions


tokenIssuer :: JSON -> Maybe StringOrURISource

Try to extract the value for the issue claim field iss from the web token in JSON form

secret :: Text -> SecretSource

Create a Secret using the given key This will currently simply wrap the given key appropriately buy may return a Nothing in the future if the key needs to adhere to a specific format and the given key is invalid.

JWT structure

claims :: JWT r -> JWTClaimsSetSource

Extract the claims set from a JSON Web Token

header :: JWT r -> JWTHeaderSource

Extract the header from a JSON Web Token

signature :: JWT r -> Maybe SignatureSource

Extract the signature from a verified JSON Web Token

JWT claims set

intDate :: NominalDiffTime -> Maybe IntDateSource

Convert the NominalDiffTime into an IntDate. Returns a Nothing if the argument is invalid (e.g. the NominalDiffTime must be convertible into a positive Integer representing the seconds since epoch).

stringOrURI :: Text -> Maybe StringOrURISource

Convert a Text into a StringOrURI. Returns a Nothing if the String cannot be converted (e.g. if the String contains a : but is *not* a valid URI).

secondsSinceEpoch :: IntDate -> NominalDiffTimeSource

Return the seconds since 1970-01-01T0:0:0Z UTC for the given IntDate

JWT header

typ :: JWTHeader -> Maybe TextSource

The typ (type) Header Parameter defined by [JWS] and [JWE] is used to declare the MIME Media Type [IANA.MediaTypes] of this complete JWT in contexts where this is useful to the application. This parameter has no effect upon the JWT processing.

cty :: JWTHeader -> Maybe TextSource

The cty (content type) Header Parameter defined by [JWS] and [JWE] is used by this specification to convey structural information about the JWT.

alg :: JWTHeader -> Maybe AlgorithmSource

The alg (algorithm) used for signing the JWT. The HS256 (HMAC using SHA-256) is the only required algorithm and the only one supported in this implementation in addition to none which means that no signature will be used.

See http://tools.ietf.org/html/draft-ietf-jose-json-web-algorithms-23#page-6


data UnverifiedJWT Source

JSON Web Token without signature verification

data VerifiedJWT Source

JSON Web Token that has been successfully verified

data Secret Source

The secret used for calculating the message signature


data JWT r Source

The JSON Web Token


Show (JWT r) 

data Algorithm Source



HMAC using SHA-256 hash algorithm

data JWTClaimsSet Source

The JWT Claims Set represents a JSON object whose members are the claims conveyed by the JWT.




iss :: Maybe StringOrURI

The iss (issuer) claim identifies the principal that issued the JWT.

sub :: Maybe StringOrURI

The sub (subject) claim identifies the principal that is the subject of the JWT.

aud :: Maybe StringOrURI

The aud (audience) claim identifies the audiences that the JWT is intended for

exp :: Maybe IntDate

The exp (expiration time) claim identifies the expiration time on or after which the JWT MUST NOT be accepted for processing. Its value MUST be a number containing an IntDate value.

nbf :: Maybe IntDate

The nbf (not before) claim identifies the time before which the JWT MUST NOT be accepted for processing.

iat :: Maybe IntDate

The iat (issued at) claim identifies the time at which the JWT was issued.

jti :: Maybe StringOrURI

The jti (JWT ID) claim provides a unique identifier for the JWT.

unregisteredClaims :: ClaimsMap

data IntDate Source

A JSON numeric value representing the number of seconds from 1970-01-01T0:0:0Z UTC until the specified UTC date/time.

data StringOrURI Source

A JSON string value, with the additional requirement that while arbitrary string values MAY be used, any value containing a : character MUST be a URI [RFC3986]. StringOrURI values are compared as case-sensitive strings with no transformations or canonicalizations applied.

data JWTHeader Source

JWT Header, describes the cryptographic operations applied to the JWT