Joken

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Documentation

A JSON Web Token (JWT) Library

The goal of this library is to provide a convenient 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:

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:

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:

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, iat, 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 initial 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:

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:

Key arguments

The family of HS algorithms use Hash-Based Message Authentication Code algorithms with the SHA (Secure Hash) hashing function. This means that it uses a shared key (the "secret") to generate a signature of the message. So, the key is a string and Jokens signer functions can receive a string.

The other algorithms are based on asymmetric cryptography. For example: RS512 is based on RSA asymmetric cryptography. This is an algorithm that works with large prime numbers multiplication. So the key must contain data about the chosen primes amongst other parameters. Therefore, we can't simply accept these parameters as string.

Similarly, as an added example, ES256 is based on a digital signing algorithm using elliptic curve keys, a kind of asymmetric cryptography. They also need information on the points used on the curve and aren't suitable to be passed as a string in free-form.

These keys have standards on how they are shared. PEM (Privacy enhanced mail) files are a common example. They have all the key information encoded in a text format. Erlang, and by consequence Elixir, has native modules for dealing with these. They reside in the :public_key module. Functions like pem_decode/1 or pem_encode/1 might be useful for handling this kind of data.

Actually, Joken depends on JOSE. There are facilities in JOSE that make the job even easier. Here is an example with an RSA key used in jwt.io:

# Suppose we have a file accessible from 'test/example_key.pem' with the following contents



#-----BEGIN RSA PRIVATE KEY-----

#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

#  -----END RSA PRIVATE KEY-----



# We can sign with this PRIVATE key using:

import Joken

key = JOSE.JWK.from_pem_file("test/example_key.pem") 



signed_token = %{ "name" => "John Doe" }

|> token

|> sign(rs256(key))

|> get_compact

In summary, what Joken expects as a key is what suits the algorithm in use. If it is:

And so on...

The definition of the parameters we expect can be seen in:

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:

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.