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A Haskell implementation of JSON Web Token (JWT).

  1. Key features
    1. Type-safety
    2. Speed and robustness
    3. Ease of use
  2. Installation
  3. Supported algorithms
    1. Example usage
      1. With secrets (HS256, HS384, HS512)
      2. With keys
  4. Usage
    1. Create a payload
      1. Namespaces
    2. Signing a token
    3. Decoding a token
  5. Supported types
    1. Flags
  6. Benchmarks
    1. Signing
    2. Decoding
  7. Not implemented
  8. Idea

Key features


Above Haskell standard type-safety, the library keeps track of public and private claim names and types. There are no user-facing HashMaps in this library! A type of a JWT token might be: Jwt '["user_name" ->> Text, "is_root" ->> Bool, "user_id" ->> UUID, "created" ->> UTCTime, "accounts" ->> NonEmpty (UUID, Text)] ('SomeNs "https://example.com").

From information encoded with precise types, it automatically derives encoders and decoders. It can also work with generic representations such as records.

Speed and robustness

libjwt-typed uses libjwt for low-level functionality. libjwt delegates cryptographic work to either GnuTLS or OpenSSL. This way, not only the most performance-sensitive features work lightning fast, they are also extremely reliable. Besides, the library does not depend on any JSON library like aeson, but it implements the necessary JSON processing in C via jsmn - which makes it even faster. Benchmarking shows that it can be over 10 times faster than other Haskell JWT libraries.

Ease of use

The library is designed for frictionless use. It can be easily extended, e.g. to add support for new types or to use custom JSON encodings compatible with other libraries you may already use in your project. Most instances can be derived automatically. The compilation errors are designed to be informational, i.e. you get Claim "user_name" does not exist in this claim set from GHC, not some 3 page long instance resolution output.


libjwt-typed is available on Hackage

You must have libjwt (preferrably the latest version) installed on your system and visible to the linker. libjwt-typed links to it at compile time. You can configure libjwt with GnuTLS or OpenSSL (it doesn't matter for lbjwt-typed which one you chose)

Supported algorithms

JWS Algorithm Description
HS256 HMAC256 HMAC with SHA-256
HS384 HMAC384 HMAC with SHA-384
HS512 HMAC512 HMAC with SHA-512
RS256 RSA256 RSASSA-PKCS1-v1_5 with SHA-256
RS384 RSA384 RSASSA-PKCS1-v1_5 with SHA-384
RS512 RSA512 RSASSA-PKCS1-v1_5 with SHA-512
ES256 ECDSA256 ECDSA with curve P-256 and SHA-256
ES384 ECDSA384 ECDSA with curve P-384 and SHA-384
ES512 ECDSA512 ECDSA with curve P-521 and SHA-512

Example usage

With secrets (HS256, HS384, HS512)

{-# LANGUAGE OverloadedStrings #-}

import Web.Libjwt

hmac512 :: Algorithm Secret
hmac512 =

A key of the same size as the hash output (for instance, 256 bits for "HS256") or larger MUST be used with these algorithms.

With keys

Obtaining or reading keys is beyond the scope of this library. It accepts PEM-encoded RSA/ECDSA keys as ByteStrings

import           Web.Libjwt

import qualified Data.ByteString.Char8         as C8

rsa2048KeyPair :: RsaKeyPair
rsa2048KeyPair =
  let private = C8.pack $ unlines
        [ "-----BEGIN RSA PRIVATE KEY-----"
        , "MIIEpgIBAAKCAQEAwCXp2P+qboao0tjUyU+D3YI+sgBn8dkGaxOvPFLBFQMNkhbL"
        -- ... 
        , "-----END RSA PRIVATE KEY-----"
      public = C8.pack $ unlines
        [ "-----BEGIN PUBLIC KEY-----"
        , "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAwCXp2P+qboao0tjUyU+D"
        -- ...
        , "-----END PUBLIC KEY-----"
  in  FromRsaPem { privKey = private, pubKey = public }

rsa512 :: Algorithm RsaKeyPair
rsa512 = RSA512 rsa2048KeyPair

ecP521KeyPair :: EcKeyPair
ecP521KeyPair =
  let private = C8.pack $ unlines
        [ "-----BEGIN EC PRIVATE KEY-----"
        , "MIHcAgEBBEIAIWLn8LIw+NC3gZJIFemY/Ku5QNNncVjNZiQdICh7KzgHPrjCrdQk"
        -- ...
        , "-----END EC PRIVATE KEY-----"
      public = C8.pack $ unlines
        [ "-----BEGIN PUBLIC KEY-----"
        -- ...
        , "-----END PUBLIC KEY-----"
  in  FromEcPem { ecPrivKey = private, ecPubKey = public }

ecdsa512 :: Algorithm EcKeyPair
ecdsa512 = ECDSA512 ecP521KeyPair

A key of size 2048 bits or larger MUST be used for RSA algorithms.

The specification defines "the use of ECDSA with the P-256 curve [secp256k1 or prime256v1] and the SHA-256 cryptographic hash function, ECDSA with the P-384 curve [secp384r1] and the SHA-384 hash function, and ECDSA with the P-521 curve [secp521r1] and the SHA-512 hash function."

As of version 0.2, you do not need private keys as long as you only decode tokens. This is obviously a type-safe feature, so you cannot pass a public-key to the signing function. Type system checks it for you.

import           Web.Libjwt

import qualified Data.ByteString.Char8         as C8

rsaPub :: RsaPubKey
rsaPub =
  let public = C8.pack $ unlines
        [ "-----BEGIN PUBLIC KEY-----"
        , "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAwCXp2P+qboao0tjUyU+D"
        -- ...
        , "-----END PUBLIC KEY-----"
  in  FromRsaPub { rsaPublicKey = public }

rsa512 :: Algorithm RsaPubKey
rsa512 = RSA512 rsaPub


Create a payload


{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE NoMonomorphismRestriction #-} -- just for sweet and short examples
{-# LANGUAGE OverloadedLabels #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards #-}

import           Web.Libjwt

import           Data.ByteString                ( ByteString )
import           Data.Default
import           Data.List.NonEmpty             ( NonEmpty(..) )
import           Data.Text                      ( Text )
import           Data.Time.Clock                ( UTCTime )
import           Data.UUID                      ( UUID )
import           GHC.Generics

import           Prelude                 hiding ( exp )

data UserClaims = UserClaims { userId :: UUID
                             , userName :: Text
                             , isRoot :: Bool
                             , createdAt :: UTCTime
                             , accounts :: NonEmpty UUID
  deriving stock (Eq, Show, Generic)
  • Direct style ```haskell

mkPayload UserClaims {..} currentTime = let now = fromUTC currentTime in def { iss = Iss (Just "myApp") , aud = Aud ["https://myApp.com"] , iat = Iat (Just now) , exp = Exp (Just $ now plusSeconds 300) , privateClaims = toPrivateClaims ( #user_name ->> userName , #is_root ->> isRoot , #user_id ->> userId , #created ->> createdAt , #accounts ->> accounts ) }

{- λ> :t mkPayload mkPayload :: UserClaims -> UTCTime -> Payload '["user_name" ->> Text, "is_root" ->> Bool, "user_id" ->> UUID, "created" ->> UTCTime, "accounts" ->> NonEmpty UUID] 'NoNs -}

* Builder (monoidal) style

mkPayload' UserClaims {..} = jwtPayload
  (withIssuer "myApp" <> withRecipient "https://myApp.com" <> setTtl 300)
  ( #user_name ->> userName
  , #is_root ->> isRoot
  , #user_id ->> userId
  , #created ->> createdAt
  , #accounts ->> accounts

λ> :t mkPayload'
  :: MonadTime m =>
     -> m (Payload
             '["user_name" ->> Text, "is_root" ->> Bool, "user_id" ->> UUID,
               "created" ->> UTCTime, "accounts" ->> NonEmpty UUID]

  • Generic style ```haskell

instance ToPrivateClaims UserClaims

mkPayload'' = jwtPayload (withIssuer "myApp" <> withRecipient "https://myApp.com" <> setTtl 300) UserClaims { userId = read "5a7c5cdd-3909-456b-9dd2-6ba84bfeeb25" , userName = "JohnDoe" , isRoot = False , createdAt = read "2020-07-31 11:45:00 UTC" , accounts = read "0bdf91cc-48bb-47f5-b633-920c34bd2352" :| [] }

#### Namespaces

To ensure that private do not collide with claims from other resources, it is recommended to give them globally unique names . This is often done through _namespacing_, i.e. prefixing the names with the URI of a resource you control. In `libjwt-typed` this is handled entirely at the type-level, and you don't need to write any code to handle this case. As you may have noticed, `Payload` types have a component of the type `NoNs`. It tracks the namespace assigned to private claims within this payload. If you change the last example to:

{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE DataKinds #-}

mkPayload''' =
      (withIssuer "myApp" <> withRecipient "https://myApp.com" <> setTtl 300)
    $ withNs
        (Ns @"https://myApp.com")
          { userId    = read "5a7c5cdd-3909-456b-9dd2-6ba84bfeeb25"
          , userName  = "JohnDoe"
          , isRoot    = False
          , createdAt = read "2020-07-31 11:45:00 UTC"
          , accounts  = read "0bdf91cc-48bb-47f5-b633-920c34bd2352" :| []

, you'll notice that the type has changed to accomodate the namespace (becoming Payload '[...] ('SomeNs "https://myApp.com")). Consequently, in the generated token "userId" becomes "https://myApp.com/userId" etc

Signing a token

token :: IO ByteString -- or any other MonadTime instance
token = getToken . sign hmac512 <$> mkPayload''

λ> token

Tip: you can inspect the above token in the JWT debugger

sign is a pure function, we only need Monad for the currentTime used to construct the payload.

Decoding a token

{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE DataKinds #-}

type MyJwt
  = Jwt
      '["userId" ->> UUID, "userName" ->> Text, "isRoot" ->> Bool, "createdAt" ->> UTCTime, "accounts" ->> NonEmpty UUID]

decodeDoNotUse :: IO (Decoded MyJwt)
decodeDoNotUse = decodeByteString hmac512 =<< token

λ> decode_do_not_use
MkDecoded {getDecoded = Jwt {header = Header {alg = HS512 (MkSecret {reveal = "MjZkMDY2OWFiZmRjYTk5YjczZWFiZjYzMmRjMzU5NDYyMjMxODBjMTg3ZmY5OTZjM2NhM2NhN2MxYzFiNDNlYjc4NTE1MjQxZGI0OWM1ZWI2ZDUyZmMzZDlhMmFiNjc5OWJlZTUxNjE2ZDRlYTNkYjU5Y2IwMDZhYWY1MjY1OTQgIC0K"}), typ = JWT}, payload = ClaimsSet {iss = Iss (Just "myApp"), sub = Sub Nothing, aud = Aud ["https://myApp.com"], exp = Exp (Just (NumericDate {secondsSinceEpoch = 1599501809})), nbf = Nbf Nothing, iat = Iat (Just (NumericDate {secondsSinceEpoch = 1599501509})), jti = Jti Nothing, privateClaims = (#userId ->> 5a7c5cdd-3909-456b-9dd2-6ba84bfeeb25, #userName ->> "JohnDoe", #isRoot ->> False, #createdAt ->> 2020-07-31 11:45:00 UTC, #accounts ->> (0bdf91cc-48bb-47f5-b633-920c34bd2352 :| []))}}}

While the structure of the JWT can be inferred when signing - this obviously is not the case when decoding. decodeByteString can't possibly know what you are going to extract from the token, so you need to give it the expected type. It can simply be type-alias like in the example above. Based on this, the correct decoder is dervied. If something goes wrong an exception will be thrown, which you can catch and inspect.

The result of this function is an instance of Decoded type. The JWT stucture wrapped in this type is guaranteed to be correct representation of the requested type with its signature checked according to your algorithm and secret/key.

IMPORTANT: Your program should always require an instance of the Validated type (see below). Decoded only means that the signature and the representation are correct, but does not verify that the token has not expired or is not intended for you etc.

To return decoded and validated structure it is better to do

decodeAndValidate :: IO (ValidationNEL ValidationFailure (Validated MyJwt))
decodeAndValidate = jwtFromByteString settings mempty hmac512 =<< token
  where settings = Settings { leeway = 5, appName = Just "https://myApp.com" }

λ> decodeAndValidate 
Success (MkValid {getValid = Jwt {header = Header {alg = HS512 (MkSecret {reveal = "MjZkMDY2OWFiZmRjYTk5YjczZWFiZjYzMmRjMzU5NDYyMjMxODBjMTg3ZmY5OTZjM2NhM2NhN2MxYzFiNDNlYjc4NTE1MjQxZGI0OWM1ZWI2ZDUyZmMzZDlhMmFiNjc5OWJlZTUxNjE2ZDRlYTNkYjU5Y2IwMDZhYWY1MjY1OTQgIC0K"}), typ = JWT}, payload = ClaimsSet {iss = Iss (Just "myApp"), sub = Sub Nothing, aud = Aud ["https://myApp.com"], exp = Exp (Just (NumericDate {secondsSinceEpoch = 1599504161})), nbf = Nbf Nothing, iat = Iat (Just (NumericDate {secondsSinceEpoch = 1599503861})), jti = Jti Nothing, privateClaims = (#userId ->> 5a7c5cdd-3909-456b-9dd2-6ba84bfeeb25, #userName ->> "JohnDoe", #isRoot ->> False, #createdAt ->> 2020-07-31 11:45:00 UTC, #accounts ->> (0bdf91cc-48bb-47f5-b633-920c34bd2352 :| []))}}})

JWT validation is a monoid. You can append additional validations based on public and private claims, for example checkIssuer "myApp" <> checkClaim (== True) #isRoot. You will certainly like the fact that private claims' types are fullly known, so you can operate on type-safe Haskell values (checkClaim ( > 0) #isRoot will not compile). The mempty validation (the default validation) checks (according to the rules in the RFC ) whether:

  • token has not expired (exp claim),
  • token is ready to use (nbf claim),
  • token is intended for you (aud claim)

Time-based validations (all predefined validations for exp, nbf and iat claims) allow for some small leeway (e.g. leeway = 5 means that the token expired less than 5 seconds ago is still considered to be valid), which can be set in ValidationSettings.

Full example with error-handling might look like:

{-# LANGUAGE ScopedTypeVariables #-}

import           Control.Arrow                  ( left )
import           Control.Exception              ( catch
                                                , displayException
import           Data.Either.Validation         ( validationToEither )

decodeAndValidateFull :: IO (Either String UserClaims)
decodeAndValidateFull =
  (   left (("Token not valid: " ++) . show)
    .   fmap toUserClaims
    .   validationToEither
    <$> decodeAndValidate
    `catch` onError
  toUserClaims = fromPrivateClaims . privateClaims . payload . getValid
  onError (e :: SomeDecodeException) =
    return $ Left $ "Cannot decode token " ++ displayException e

λ> decodeAndValidateFull 
Right (UserClaims {userId = 5a7c5cdd-3909-456b-9dd2-6ba84bfeeb25, userName = "JohnDoe", isRoot = False, createdAt = 2020-07-31 11:45:00 UTC, accounts = 0bdf91cc-48bb-47f5-b633-920c34bd2352 :| []})

Supported types

The following types are currently supported:

  • ByteString
  • String
  • Text
  • Libjwt.ASCII (for marking strings as ASCII only)
  • Libjwt.JsonByteString (for working with pure JSON)
  • Bool
  • Libjwt.NumericDate (POSIX timestamps)
  • Libjwt.Flag (for simple sum types)
  • Int
  • UUID
  • UTCTime, ZonedTime, LocalTime, Day
  • Maybes of the above types
  • lists of the above types and lists of tuples created from them
  • NonEmpty lists of the above types


Flags provide a way to automatically encode and decode simple sum types.

data Scope = Login | Extended | UserRead | UserWrite | AccountRead | AccountWrite
  deriving stock (Show, Eq, Generic)

instance AFlag Scope

Now, you can use Flag Scope in JWT claims, e.g.

mkPayload' UserClaims {..} = jwtPayload
  (withIssuer "myApp" <> withRecipient "https://myApp.com" <> setTtl 300)
  ( #user_name ->> userName
  , #is_root ->> isRoot
  , #user_id ->> userId
  , #created ->> createdAt
  , #accounts ->> accounts
  , #scope ->> Flag Login


Full result sets (graphical HTML reports) are available here.

Code can be found here. Benchmarking is undoubtedly hard - if you think something can be improved, please make a PR.

The Benchmarks compare libjwt-typed to jose in different hopefully real-world use cases. All the results below were obtained on a 6-Core Intel Core i7-9750H; 32 GB RAM; GHC 8.10.2 (compiled with -O2; RTS options: -N -ki2k -A512m -n32m); libjwt built with GnuTLS using GCC 10.2.0


Measuring going from data to a fully signed, ready to send over-the-wire token

When signing an "empty" token using SHA-512 i.e. something like

  "iat": 1599531131,
  "nbf": 1599531131,
  "exp": 1599531431,
  "sub": "c5caab61-3ee4-49ab-86e6-b6ac292901f7",
  "aud": ["https://example.com"],
  "iss": "benchmarks"
what libjwt jose speedup
mean 9.05 μs (± 277 ns) 163 μs (± 5.39 μs) 18x

For more complex tokens i.e. something like

  "iat": 1599531131,
  "nbf": 1599531131,
  "exp": 1599531431,
  "sub": "c5caab61-3ee4-49ab-86e6-b6ac292901f7",
  "aud": ["https://example.com"],
  "iss": "benchmarks",
  "user_name": "E\\129057~[lzR64FhhdhrlUMH0A",
  "is_root": true,
  "client_id": "b659f842-5d78-4da1-9891-8aaa4ac3983b",
  "created": "2020-09-08 02:12:11.099106573 UTC",
  "accounts": [
    ["8aa634fb-8cc4-44cb-84ec-9eb6c78834e1", "k"],
    ["da8b0ff6-a32c-43d0-bd89-1a63273945e0", ")`"],
    ["219f30da-c474-4f23-af6a-495b1034e02f", "J"]
  "emails": ["0g([email protected]", "[email protected]"]
what libjwt jose speedup
mean 35.3 μs (± 111 ns) 521 μs (± 9.45 μs) 14x

When signing using elliptic-curve cryptography: ECDSA256

what libjwt jose speedup
mean (simple) 76.8 μs (± 296 ns) 1.16 ms (± 7.5 μs) 15x
mean (complex) 111 μs (± 495 ns) 1.53 ms (± 12.4 μs) 13x

and ECDSA512

what libjwt jose speedup
mean (simple) 266 μs (± 1.22 μs) 3.92 ms (± 27.8 μs) 14x
mean (complex) 300 μs (± 831 ns) 4.25 ms (± 24.1 μs) 14x

And finally using the RSA (RSASSA-PKCS1-v1_5 using SHA-512)

what libjwt jose speedup
mean (simple) 1.39 ms (± 4.83 μs) 1.03 ms (± 7.86 μs) 0.7x
mean (complex) 1.42 ms (± 6.70 μs) 1.39 ms (± 12.3 μs) 0.9x

This is the only time jose is faster (congrats!). libjwt-typed is slower probably because it doesn't store private key parameters. This is something thaht needs to be improved.


Here going from a ByteString token back to the data is measured. When I say "to the data" I mean user-types, not aeson values. This is where libjwt-typed has considerable leverage as it doesn't use any intermediate form, but I think it is fair as users will eventually have to parse data anyway.

Using HMAC512

what libjwt jose speedup
mean (simple) 9.23 μs (± 134 ns) 128 μs (± 2.54 μs) 13x
mean (complex) 63.3 μs (± 736 ns) 391 μs (± 5.84 μs) 6x

Using ECDSA256

what libjwt jose speedup
mean (simple) 187 μs (± 551 ns) 1.24 ms (± 8.54 μs) 6x
mean (complex) 241 μs (± 578 ns) 1.52 ms (± 6.50 μs) 6x

Using ECDSA512

what libjwt jose speedup
mean (simple) 746 μs (± 2.78 μs) 4.40 ms (± 12.3 μs) 5x
mean (complex) 797 μs (± 1.67 μs) 4.78 ms (± 28.2 μs) 6x

And finally RSA

what libjwt jose speedup
mean (simple) 39.3 μs (± 170 ns) 137 μs (± 2.97 μs) 3x
mean (complex) 97.3 μs (± 503 ns) 398 μs (± 5.58 μs) 4x

Not implemented

  • JWT header can only contain alg and typ (everything else is ignored). This decision is partly because of the belief that you rarely need to complicate the header, and partly because of the limiation of libjwt which prevents the header from being checked before decoding (this is done in one step). For this reason, things like selecting keys based on the header cannot be easily implemented.


The idea for this lib comes from my talk "Building a web library using super hard Haskell" at the Haskell Love Conference

*Note that all licence references and agreements mentioned in the libjwt-typed README section above are relevant to that project's source code only.