A Haskell implementation of the JSON Object Signing and Encryption (JOSE) specifications and the related JWT specification, as used, for example, in OpenID Connect.
The JWT specification was split into JWS and JWE during its development so does not contain much. A JWT is either a JWS or a JWE depending on whether it is signed or encrypted. It is encoded as a sequence of base64 strings separated by '.' characters [1].
Technically, the content of a JWT should be JSON (unless it's a nested JWT), but this library doesn't care - it only requires a bytestring. The application should verify that the content is valid. Exactly what that means will depend on what you are using JWTs for.
You can either use the high-level encode and decode functions in the Jwt module or specific functions in the Jws and Jwe modules.
The following examples can be entered directly into ghci. Use
> :set -XOverloadedStrings
to begin with.
HMAC is a good choice when both signer and verifier have a copy of the key.
> import Jose.Jws (hmacEncode, hmacDecode)
> import Jose.Jwa (JwsAlg(HS256))
>
> hmacEncode HS256 "aRANDOMlygeneratedkey" "my JSON message"
Right (Jwt {unJwt = "eyJhbGciOiJIUzI1NiJ9.bXkgSlNPTiBtZXNzYWdl.lTJx7ECLwYF3P7WbrrUpcp_2SdLiFXaDwK-PXcipt5Q"})
> hmacDecode "aRANDOMlygeneratedkey" "eyJhbGciOiJIUzI1NiJ9.bXkgSlNPTiBtZXNzYWdl.lTJx7ECLwYF3P7WbrrUpcp_2SdLiFXaDwK-PXcipt5Q"
Right (JwsHeader {jwsAlg = HS256, jwsTyp = Nothing, jwsCty = Nothing, jwsKid = Nothing},"my JSON message")
Trying to decode with a different key would return a Left BadSignature [2].
Some situations require the use of public key cryptography for signing. For example, only a trusted party is allowed to create a signed token, but it must be verified by others.
Elliptic-curve EdDSA signing and verification are supported as defined in RFC 8037, as well as the older RSA JWS algorithms.
> import Jose.Jwt
> import Jose.Jwk
> import Jose.Jwa (JwsAlg(EdDSA))
> import Data.ByteString (ByteString)
> import Data.Aeson (decodeStrict)
>
> jsonJwk = "{\"kty\":\"OKP\", \"crv\":\"Ed25519\", \"d\":\"nWGxne_9WmC6hEr0kuwsxERJxWl7MmkZcDusAxyuf2A\", \"x\":\"11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwIaaPcHURo\"}" :: ByteString
> Just jwk = decodeStrict jsonJwk :: Maybe Jwk
> Jose.Jwt.encode [jwk] (JwsEncoding EdDSA) (Claims "public claims")
Right (Jwt {unJwt = "eyJhbGciOiJFZERTQSJ9.cHVibGljIGNsYWltcw.xYekeeGSQVpnQbl16lOCqFcmYsUj3goSTrZ4UBQqogjHLrvFUaVJ_StBqly-Tb-0xvayjUMM4INYBTwFMt_xAQ"})
To verify the JWT you would use the Jose.Jwt.decode function with the corresponding public key.
More examples can be found in the package documentation.
[1] This is now referred to as "compact serialization". The additional "JSON serialization" is not supported in this library.
[2] Note that a real key for HMAC256 should be a much longer, random string of bytes. See, for example, this stackexchange answer.