Joken

Documentation

A JSON Web Token (JWT) Library

The goal of this library is to provide a convienent way to create, sign, verify, and validate JWTs while allowing the flexibility to customize each step along the way. This library also includes a Plug for checking tokens as well.

Supports the following algorithms:

• ES256
• ES384
• ES512
• HS256
• HS384
• HS512
• PS256 ¹
• PS384 ¹
• PS512 ¹
• RS256
• RS384
• RS512
• Ed25519
• Ed25519ph
• Ed448ph
• Ed448

¹ Implemented mostly in pure Erlang. May be less performant than other supported signature algorithms. See jose JWS algorithm support for more information.

Joken allows you to use any claims you wish, but has convenience methods for the claims listed in the specification. These claims are listed below:

• exp: Expiration
• nbf: Not Before
• aud: Audience
• iss: Issuer
• sub: Subject
• iat: Issued At
• jti: JSON Token ID

For a more in depth description of each claim, please see the reference specification here.

You can view the changelog here or on the official documentation in the "Pages" section.

Usage

All you need to generate a token is a Joken.Token struct with proper values. There you can set:

• json_module: choose your JSON library (currently supports Poison | JSX)
• signer: a map that tells the underlying system how to sign and verify your tokens
• validations: a map of claims keys to function validations
• claims: the map of values you want encoded in a token
• claims_generation: a map of functions called when signing to generate dynamic values
• token: the compact representation of a JWT token
• error: message indicating why a sign/verify operation failed

To help you fill that configuration struct properly, use the functions in the Joken module.

Joken allows for customization of tokens, but also provides some defaults.

To create a token with default generator for claims exp, iaf, and nbf, and to use Poison as the json serializer:

import Joken

my_token = token
|> with_signer(hs256("my_secret"))

To create a function with an inital map of claims:

import Joken

my_token = %{user_id: 1}
|> token
|> with_signer(hs256("my_secret"))

Here is an example of adding a custom validator for the claim:

import Joken

my_token = %{user_id: 1}
|> token
|> with_validation("user_id", &(&1 == 1))

To sign a token, use the sign function. The get_compact function will return the token in its binary form:

import Joken

my_token = %{user_id: 1}
|> token
|> with_validation("user_id", &(&1 == 1))
|> with_signer(hs256("my_secret"))
|> sign
|> get_compact

Verifying a token works in the same way. First, create a token using the compact form and verify it. verify will return the Joken.Token struct with the claims property filled with the claims from the token if verified. Otherwise, the error property will have the error:

import Joken

my_verified_token = "some_token"
|> token
|> with_validation("user_id", &(&1 == 1))
|> with_signer(hs256("my_secret"))
|> verify

There are other options and helper functions available. See the docs of the Joken module for a complete documentation.

Plug

Joken also comes with a Plug for verifying JWTs in web applications.

There are two possible scenarios:

1. Same configuration for all routes
2. Per route configuration

In the first scenario just add this plug before the dispatch plug.

  defmodule MyRouter do
    use Plug.Router

    plug Joken.Plug, verify: &MyRouter.verify_function/0
    plug :match
    plug :dispatch

    post "/user" do
      # will only execute here if token is present and valid
    end

    match _ do
      # will only execute here if token is present and valid
    end

    def verify_function() do
      %Joken.Token{}
      |> Joken.with_signer(hs256("secret"))
      |> Joken.with_sub(1234567890)
    end
  end

In the second scenario, you will need at least plug ~> 0.14 in your deps. Then you must plug this AFTER :match and BEFORE :dispatch.

  defmodule MyRouter do
    use Plug.Router

    # route options
    @skip_token_verification %{joken_skip: true}
    
    @custom_token_verification %{joken_verify: %MyRouter.is_not_subject/0}

    plug :match
    plug Joken.Plug, verify: &MyRouter.verify_function/0       
    plug :dispatch

    post "/user" do
      # will only execute here if token is present and valid
    end
    
    post "/endpoint", private: @custom_token_verification do
      # will only execute here if token is present and valid 
      # using the function `is_not_subject/0`
    end

    # see options section below
    match _, private: @skip_token_verification do
      # will NOT try to validate a token
    end
    
    def verify_function() do
      %Joken.Token{}
      |> Joken.with_signer(hs256("secret"))
      |> Joken.with_sub(1234567890)
    end
    
    def is_not_subject() do
      %Joken.Token{}
      |> Joken.with_validation("sub", &(&1 != 1234567890))
      |> Joken.with_signer(hs256("secret"))
    end
  end

For more examples, look in our tests for more usage scenarios.

Options

This plug accepts the following options in its initialization:

• verify (required): a function used to verify the token. The function must at least specify algorithm used and your secret using the with_signer function (see above). Must return a Token.

• on_error (optional): a function that accepts conn and message as parameters. Must return a tuple containing the conn and a binary representing the 401 response. If it's a map, it's turned into json, otherwise, it is returned as is.

When using this with per route options you must pass a private map of options to the route. The keys that Joken will look for in that map are:

• joken_skip: skips token validation. true or false

• joken_verify: Same as verify above. Overrides verify if defined on the Plug

• joken_on_error: Same as on_error above. Overrides on_error if defined on the Plug

Native crypto

Joken is based on cryptography implemented by the erlang-jose project. One of the features it provides is the ability to auto detect the presence of native crypto libraries with a NIF (Erlang's Native Implemented Function) interface. Some of these libraries are:

• erlang-libsodium: provides native implemented crypto for Ed25519 and Ed25519ph
• erlang-keccakf1600: provides SHA-3 NIFs
• erlang-libdecaf: provides ed448goldilocks NIFs

Joken inherits that auto discovery feature. So, in order to increase speed in scenarios that you are using these crypto libraries, all you need to do is add them as dependencies:

defp deps do
  [
    {:joken, "~> 1.1"},
    {:libsodium, "~> 0.0.3"},
    {:keccakf1600, "~> 0.0.1"},
    {:libdecaf, "~> 0.0.1"}
  ]
end

Be advised though that this is a work in progress by @potatosalad.