# JWT

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A ruby implementation of the [RFC 7519 OAuth JSON Web Token (JWT)](https://tools.ietf.org/html/rfc7519) standard.

If you have further questions related to development or usage, join us: [ruby-jwt google group](https://groups.google.com/forum/#!forum/ruby-jwt).

## Announcements
* Ruby 2.4 support was dropped in version 2.4.0
* Ruby 1.9.3 support was dropped at December 31st, 2016.
* Version 1.5.3 yanked. See: [#132](https://github.com/jwt/ruby-jwt/issues/132) and [#133](https://github.com/jwt/ruby-jwt/issues/133)

See [CHANGELOG.md](CHANGELOG.md) for a complete set of changes.

## Sponsors

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|![auth0 logo](https://user-images.githubusercontent.com/83319/31722733-de95bbde-b3ea-11e7-96bf-4f4e8f915588.png)|If you want to quickly add secure token-based authentication to Ruby projects, feel free to check Auth0's Ruby SDK and free plan at [auth0.com/developers](https://auth0.com/developers?utm_source=GHsponsor&utm_medium=GHsponsor&utm_campaign=rubyjwt&utm_content=auth)|

## Installing

### Using Rubygems:
```bash
gem install jwt
```

### Using Bundler:
Add the following to your Gemfile
```
gem 'jwt'
```
And run `bundle install`

## Algorithms and Usage

The JWT spec supports NONE, HMAC, RSASSA, ECDSA and RSASSA-PSS algorithms for cryptographic signing. Currently the jwt gem supports NONE, HMAC, RSASSA and ECDSA. If you are using cryptographic signing, you need to specify the algorithm in the options hash whenever you call JWT.decode to ensure that an attacker [cannot bypass the algorithm verification step](https://auth0.com/blog/critical-vulnerabilities-in-json-web-token-libraries/). **It is strongly recommended that you hard code the algorithm, as you may leave yourself vulnerable by dynamically picking the algorithm**

See: [ JSON Web Algorithms (JWA) 3.1. "alg" (Algorithm) Header Parameter Values for JWS](https://tools.ietf.org/html/rfc7518#section-3.1)

### Deprecation warnings

Deprecation warnings are logged once (`:once` option) by default to avoid spam in logs. Other options are `:silent` to completely silence warnings and `:warn` to log every time a deprecated path is executed.

```ruby
  JWT.configuration.deprecation_warnings = :warn # default is :once
```

### Base64 decoding

In the past the gem has been supporting the Base64 decoding specified in [RFC2045](https://www.rfc-editor.org/rfc/rfc2045) allowing newlines and blanks in the base64 encoded payload. In future versions base64 decoding will be stricter and only comply to [RFC4648](https://www.rfc-editor.org/rfc/rfc4648).

The stricter base64 decoding when processing tokens can be done via the `strict_base64_decoding` configuration accessor.
```ruby
  JWT.configuration.strict_base64_decoding = true # default is false
```

### **NONE**

* none - unsigned token

```ruby
require 'jwt'

payload = { data: 'test' }

# IMPORTANT: set nil as password parameter
token = JWT.encode payload, nil, 'none'

# eyJhbGciOiJub25lIn0.eyJkYXRhIjoidGVzdCJ9.
puts token

# Set password to nil and validation to false otherwise this won't work
decoded_token = JWT.decode token, nil, false

# Array
# [
#   {"data"=>"test"}, # payload
#   {"alg"=>"none"} # header
# ]
puts decoded_token
```

### **HMAC**

* HS256 - HMAC using SHA-256 hash algorithm
* HS384 - HMAC using SHA-384 hash algorithm
* HS512 - HMAC using SHA-512 hash algorithm

```ruby
# The secret must be a string. With OpenSSL 3.0/openssl gem `<3.0.1`, JWT::DecodeError will be raised if it isn't provided.
hmac_secret = 'my$ecretK3y'

token = JWT.encode payload, hmac_secret, 'HS256'

# eyJhbGciOiJIUzI1NiJ9.eyJkYXRhIjoidGVzdCJ9.pNIWIL34Jo13LViZAJACzK6Yf0qnvT_BuwOxiMCPE-Y
puts token

decoded_token = JWT.decode token, hmac_secret, true, { algorithm: 'HS256' }

# Array
# [
#   {"data"=>"test"}, # payload
#   {"alg"=>"HS256"} # header
# ]
puts decoded_token
```

### **RSA**

* RS256 - RSA using SHA-256 hash algorithm
* RS384 - RSA using SHA-384 hash algorithm
* RS512 - RSA using SHA-512 hash algorithm

```ruby
rsa_private = OpenSSL::PKey::RSA.generate 2048
rsa_public = rsa_private.public_key

token = JWT.encode payload, rsa_private, 'RS256'

# eyJhbGciOiJSUzI1NiJ9.eyJkYXRhIjoidGVzdCJ9.GplO4w1spRgvEJQ3-FOtZr-uC8L45Jt7SN0J4woBnEXG_OZBSNcZjAJWpjadVYEe2ev3oUBFDYM1N_-0BTVeFGGYvMewu8E6aMjSZvOpf1cZBew-Vt4poSq7goG2YRI_zNPt3af2lkPqXD796IKC5URrEvcgF5xFQ-6h07XRDpSRx1ECrNsUOt7UM3l1IB4doY11GzwQA5sHDTmUZ0-kBT76ZMf12Srg_N3hZwphxBtudYtN5VGZn420sVrQMdPE_7Ni3EiWT88j7WCr1xrF60l8sZT3yKCVleG7D2BEXacTntB7GktBv4Xo8OKnpwpqTpIlC05dMowMkz3rEAAYbQ
puts token

decoded_token = JWT.decode token, rsa_public, true, { algorithm: 'RS256' }

# Array
# [
#   {"data"=>"test"}, # payload
#   {"alg"=>"RS256"} # header
# ]
puts decoded_token
```

### **ECDSA**

* ES256 - ECDSA using P-256 and SHA-256
* ES384 - ECDSA using P-384 and SHA-384
* ES512 - ECDSA using P-521 and SHA-512
* ES256K - ECDSA using P-256K and SHA-256

```ruby
ecdsa_key = OpenSSL::PKey::EC.generate('prime256v1')

token = JWT.encode payload, ecdsa_key, 'ES256'

# eyJhbGciOiJFUzI1NiJ9.eyJkYXRhIjoidGVzdCJ9.AlLW--kaF7EX1NMX9WJRuIW8NeRJbn2BLXHns7Q5TZr7Hy3lF6MOpMlp7GoxBFRLISQ6KrD0CJOrR8aogEsPeg
puts token

decoded_token = JWT.decode token, ecdsa_key, true, { algorithm: 'ES256' }

# Array
# [
#    {"test"=>"data"}, # payload
#    {"alg"=>"ES256"} # header
# ]
puts decoded_token
```

### **EDDSA**

In order to use this algorithm you need to add the `RbNaCl` gem to you `Gemfile`.

```ruby
gem 'rbnacl'
```

For more detailed installation instruction check the official [repository](https://github.com/RubyCrypto/rbnacl) on GitHub.

* ED25519

```ruby
private_key = RbNaCl::Signatures::Ed25519::SigningKey.new('abcdefghijklmnopqrstuvwxyzABCDEF')
public_key = private_key.verify_key
token = JWT.encode payload, private_key, 'ED25519'

# eyJhbGciOiJFRDI1NTE5In0.eyJkYXRhIjoidGVzdCJ9.6xIztXyOupskddGA_RvKU76V9b2dCQUYhoZEVFnRimJoPYIzZ2Fm47CWw8k2NTCNpgfAuxg9OXjaiVK7MvrbCQ
puts token

decoded_token = JWT.decode token, public_key, true, { algorithm: 'ED25519' }
# Array
# [
#  {"test"=>"data"}, # payload
#  {"alg"=>"ED25519"} # header
# ]

```

### **RSASSA-PSS**

In order to use this algorithm you need to add the `openssl` gem to your `Gemfile` with a version greater or equal to `2.1`.

```ruby
gem 'openssl', '~> 2.1'
```

* PS256 - RSASSA-PSS using SHA-256 hash algorithm
* PS384 - RSASSA-PSS using SHA-384 hash algorithm
* PS512 - RSASSA-PSS using SHA-512 hash algorithm

```ruby
rsa_private = OpenSSL::PKey::RSA.generate 2048
rsa_public = rsa_private.public_key

token = JWT.encode payload, rsa_private, 'PS256'

# eyJhbGciOiJQUzI1NiJ9.eyJkYXRhIjoidGVzdCJ9.KEmqagMUHM-NcmXo6818ZazVTIAkn9qU9KQFT1c5Iq91n0KRpAI84jj4ZCdkysDlWokFs3Dmn4MhcXP03oJKLFgnoPL40_Wgg9iFr0jnIVvnMUp1kp2RFUbL0jqExGTRA3LdAhuvw6ZByGD1bkcWjDXygjQw-hxILrT1bENjdr0JhFd-cB0-ps5SB0mwhFNcUw-OM3Uu30B1-mlFaelUY8jHJYKwLTZPNxHzndt8RGXF8iZLp7dGb06HSCKMcVzhASGMH4ZdFystRe2hh31cwcvnl-Eo_D4cdwmpN3Abhk_8rkxawQJR3duh8HNKc4AyFPo7SabEaSu2gLnLfN3yfg
puts token

decoded_token = JWT.decode token, rsa_public, true, { algorithm: 'PS256' }

# Array
# [
#   {"data"=>"test"}, # payload
#   {"alg"=>"PS256"} # header
# ]
puts decoded_token
```

### **Custom algorithms**

An object implementing custom signing or verification behaviour can be passed in the `algorithm` option when encoding and decoding. The given object needs to implement the method `valid_alg?` and `verify` and/or `alg` and `sign`, depending if object is used for encoding or decoding.

```ruby
module CustomHS512Algorithm
  def self.alg
    'HS512'
  end

  def self.valid_alg?(alg_to_validate)
    alg_to_validate == alg
  end

  def self.sign(data:, signing_key:)
    OpenSSL::HMAC.digest(OpenSSL::Digest.new('sha512'), data, signing_key)
  end

  def self.verify(data:, signature:, verification_key:)
    ::OpenSSL.secure_compare(sign(data: data, signing_key: verification_key), signature)
  end
end

token = ::JWT.encode({'pay' => 'load'}, 'secret', CustomHS512Algorithm)
payload, header = ::JWT.decode(token, 'secret', true, algorithm: CustomHS512Algorithm)
```

## Support for reserved claim names
JSON Web Token defines some reserved claim names and defines how they should be
used. JWT supports these reserved claim names:

 - 'exp' (Expiration Time) Claim
 - 'nbf' (Not Before Time) Claim
 - 'iss' (Issuer) Claim
 - 'aud' (Audience) Claim
 - 'jti' (JWT ID) Claim
 - 'iat' (Issued At) Claim
 - 'sub' (Subject) Claim

## Add custom header fields
Ruby-jwt gem supports custom [header fields](https://tools.ietf.org/html/rfc7519#section-5)
To add custom header fields you need to pass `header_fields` parameter

```ruby
token = JWT.encode payload, key, algorithm='HS256', header_fields={}
```

**Example:**

```ruby
require 'jwt'

payload = { data: 'test' }

# IMPORTANT: set nil as password parameter
token = JWT.encode payload, nil, 'none', { typ: 'JWT' }

# eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.eyJkYXRhIjoidGVzdCJ9.
puts token

# Set password to nil and validation to false otherwise this won't work
decoded_token = JWT.decode token, nil, false

# Array
# [
#   {"data"=>"test"}, # payload
#   {"typ"=>"JWT", "alg"=>"none"} # header
# ]
puts decoded_token
```

### Expiration Time Claim

From [Oauth JSON Web Token 4.1.4. "exp" (Expiration Time) Claim](https://tools.ietf.org/html/rfc7519#section-4.1.4):

> The `exp` (expiration time) claim identifies the expiration time on or after which the JWT MUST NOT be accepted for processing. The processing of the `exp` claim requires that the current date/time MUST be before the expiration date/time listed in the `exp` claim. Implementers MAY provide for some small `leeway`, usually no more than a few minutes, to account for clock skew. Its value MUST be a number containing a ***NumericDate*** value. Use of this claim is OPTIONAL.

**Handle Expiration Claim**

```ruby
exp = Time.now.to_i + 4 * 3600
exp_payload = { data: 'data', exp: exp }

token = JWT.encode exp_payload, hmac_secret, 'HS256'

begin
  decoded_token = JWT.decode token, hmac_secret, true, { algorithm: 'HS256' }
rescue JWT::ExpiredSignature
  # Handle expired token, e.g. logout user or deny access
end
```

The Expiration Claim verification can be disabled.
```ruby
# Decode token without raising JWT::ExpiredSignature error
JWT.decode token, hmac_secret, true, { verify_expiration: false, algorithm: 'HS256' }
```

**Adding Leeway**

```ruby
exp = Time.now.to_i - 10
leeway = 30 # seconds

exp_payload = { data: 'data', exp: exp }

# build expired token
token = JWT.encode exp_payload, hmac_secret, 'HS256'

begin
  # add leeway to ensure the token is still accepted
  decoded_token = JWT.decode token, hmac_secret, true, { exp_leeway: leeway, algorithm: 'HS256' }
rescue JWT::ExpiredSignature
  # Handle expired token, e.g. logout user or deny access
end
```

### Not Before Time Claim

From [Oauth JSON Web Token 4.1.5. "nbf" (Not Before) Claim](https://tools.ietf.org/html/rfc7519#section-4.1.5):

> The `nbf` (not before) claim identifies the time before which the JWT MUST NOT be accepted for processing. The processing of the `nbf` claim requires that the current date/time MUST be after or equal to the not-before date/time listed in the `nbf` claim. Implementers MAY provide for some small `leeway`, usually no more than a few minutes, to account for clock skew. Its value MUST be a number containing a ***NumericDate*** value. Use of this claim is OPTIONAL.

**Handle Not Before Claim**

```ruby
nbf = Time.now.to_i - 3600
nbf_payload = { data: 'data', nbf: nbf }

token = JWT.encode nbf_payload, hmac_secret, 'HS256'

begin
  decoded_token = JWT.decode token, hmac_secret, true, { algorithm: 'HS256' }
rescue JWT::ImmatureSignature
  # Handle invalid token, e.g. logout user or deny access
end
```

The Not Before Claim verification can be disabled.
```ruby
# Decode token without raising JWT::ImmatureSignature error
JWT.decode token, hmac_secret, true, { verify_not_before: false, algorithm: 'HS256' }
```

**Adding Leeway**

```ruby
nbf = Time.now.to_i + 10
leeway = 30

nbf_payload = { data: 'data', nbf: nbf }

# build expired token
token = JWT.encode nbf_payload, hmac_secret, 'HS256'

begin
  # add leeway to ensure the token is valid
  decoded_token = JWT.decode token, hmac_secret, true, { nbf_leeway: leeway, algorithm: 'HS256' }
rescue JWT::ImmatureSignature
  # Handle invalid token, e.g. logout user or deny access
end
```

### Issuer Claim

From [Oauth JSON Web Token 4.1.1. "iss" (Issuer) Claim](https://tools.ietf.org/html/rfc7519#section-4.1.1):

> The `iss` (issuer) claim identifies the principal that issued the JWT. The processing of this claim is generally application specific. The `iss` value is a case-sensitive string containing a ***StringOrURI*** value. Use of this claim is OPTIONAL.

You can pass multiple allowed issuers as an Array, verification will pass if one of them matches the `iss` value in the payload.

```ruby
iss = 'My Awesome Company Inc. or https://my.awesome.website/'
iss_payload = { data: 'data', iss: iss }

token = JWT.encode iss_payload, hmac_secret, 'HS256'

begin
  # Add iss to the validation to check if the token has been manipulated
  decoded_token = JWT.decode token, hmac_secret, true, { iss: iss, verify_iss: true, algorithm: 'HS256' }
rescue JWT::InvalidIssuerError
  # Handle invalid token, e.g. logout user or deny access
end
```

You can also pass a Regexp or Proc (with arity 1), verification will pass if the regexp matches or the proc returns truthy.
On supported ruby versions (>= 2.5) you can also delegate to methods, on older versions you will have
to convert them to proc (using `to_proc`)

```ruby
JWT.decode token, hmac_secret, true,
           iss: %r'https://my.awesome.website/',
           verify_iss: true,
           algorithm: 'HS256'
```

```ruby
JWT.decode token, hmac_secret, true,
           iss: ->(issuer) { issuer.start_with?('My Awesome Company Inc') },
           verify_iss: true,
           algorithm: 'HS256'
```

```ruby
JWT.decode token, hmac_secret, true,
           iss: method(:valid_issuer?),
           verify_iss: true,
           algorithm: 'HS256'

# somewhere in the same class:
def valid_issuer?(issuer)
  # custom validation
end
```

### Audience Claim

From [Oauth JSON Web Token 4.1.3. "aud" (Audience) Claim](https://tools.ietf.org/html/rfc7519#section-4.1.3):

> The `aud` (audience) claim identifies the recipients that the JWT is intended for. Each principal intended to process the JWT MUST identify itself with a value in the audience claim. If the principal processing the claim does not identify itself with a value in the `aud` claim when this claim is present, then the JWT MUST be rejected. In the general case, the `aud` value is an array of case-sensitive strings, each containing a ***StringOrURI*** value. In the special case when the JWT has one audience, the `aud` value MAY be a single case-sensitive string containing a ***StringOrURI*** value. The interpretation of audience values is generally application specific. Use of this claim is OPTIONAL.

```ruby
aud = ['Young', 'Old']
aud_payload = { data: 'data', aud: aud }

token = JWT.encode aud_payload, hmac_secret, 'HS256'

begin
  # Add aud to the validation to check if the token has been manipulated
  decoded_token = JWT.decode token, hmac_secret, true, { aud: aud, verify_aud: true, algorithm: 'HS256' }
rescue JWT::InvalidAudError
  # Handle invalid token, e.g. logout user or deny access
  puts 'Audience Error'
end
```

### JWT ID Claim

From [Oauth JSON Web Token 4.1.7. "jti" (JWT ID) Claim](https://tools.ietf.org/html/rfc7519#section-4.1.7):

> The `jti` (JWT ID) claim provides a unique identifier for the JWT. The identifier value MUST be assigned in a manner that ensures that there is a negligible probability that the same value will be accidentally assigned to a different data object; if the application uses multiple issuers, collisions MUST be prevented among values produced by different issuers as well. The `jti` claim can be used to prevent the JWT from being replayed. The `jti` value is a case-sensitive string. Use of this claim is OPTIONAL.

```ruby
# Use the secret and iat to create a unique key per request to prevent replay attacks
jti_raw = [hmac_secret, iat].join(':').to_s
jti = Digest::MD5.hexdigest(jti_raw)
jti_payload = { data: 'data', iat: iat, jti: jti }

token = JWT.encode jti_payload, hmac_secret, 'HS256'

begin
  # If :verify_jti is true, validation will pass if a JTI is present
  #decoded_token = JWT.decode token, hmac_secret, true, { verify_jti: true, algorithm: 'HS256' }
  # Alternatively, pass a proc with your own code to check if the JTI has already been used
  decoded_token = JWT.decode token, hmac_secret, true, { verify_jti: proc { |jti| my_validation_method(jti) }, algorithm: 'HS256' }
  # or
  decoded_token = JWT.decode token, hmac_secret, true, { verify_jti: proc { |jti, payload| my_validation_method(jti, payload) }, algorithm: 'HS256' }
rescue JWT::InvalidJtiError
  # Handle invalid token, e.g. logout user or deny access
  puts 'Error'
end
```

### Issued At Claim

From [Oauth JSON Web Token 4.1.6. "iat" (Issued At) Claim](https://tools.ietf.org/html/rfc7519#section-4.1.6):

> The `iat` (issued at) claim identifies the time at which the JWT was issued. This claim can be used to determine the age of the JWT. The `leeway` option is not taken into account when verifying this claim. The `iat_leeway` option was removed in version 2.2.0. Its value MUST be a number containing a ***NumericDate*** value. Use of this claim is OPTIONAL.

**Handle Issued At Claim**

```ruby
iat = Time.now.to_i
iat_payload = { data: 'data', iat: iat }

token = JWT.encode iat_payload, hmac_secret, 'HS256'

begin
  # Add iat to the validation to check if the token has been manipulated
  decoded_token = JWT.decode token, hmac_secret, true, { verify_iat: true, algorithm: 'HS256' }
rescue JWT::InvalidIatError
  # Handle invalid token, e.g. logout user or deny access
end
```

### Subject Claim

From [Oauth JSON Web Token 4.1.2. "sub" (Subject) Claim](https://tools.ietf.org/html/rfc7519#section-4.1.2):

> The `sub` (subject) claim identifies the principal that is the subject of the JWT. The Claims in a JWT are normally statements about the subject. The subject value MUST either be scoped to be locally unique in the context of the issuer or be globally unique. The processing of this claim is generally application specific. The sub value is a case-sensitive string containing a ***StringOrURI*** value. Use of this claim is OPTIONAL.

```ruby
sub = 'Subject'
sub_payload = { data: 'data', sub: sub }

token = JWT.encode sub_payload, hmac_secret, 'HS256'

begin
  # Add sub to the validation to check if the token has been manipulated
  decoded_token = JWT.decode token, hmac_secret, true, { sub: sub, verify_sub: true, algorithm: 'HS256' }
rescue JWT::InvalidSubError
  # Handle invalid token, e.g. logout user or deny access
end
```

### Finding a Key

To dynamically find the key for verifying the JWT signature, pass a block to the decode block. The block receives headers and the original payload as parameters. It should return with the key to verify the signature that was used to sign the JWT.

```ruby
issuers = %w[My_Awesome_Company1 My_Awesome_Company2]
iss_payload = { data: 'data', iss: issuers.first }

secrets = { issuers.first => hmac_secret, issuers.last => 'hmac_secret2' }

token = JWT.encode iss_payload, hmac_secret, 'HS256'

begin
  # Add iss to the validation to check if the token has been manipulated
  decoded_token = JWT.decode(token, nil, true, { iss: issuers, verify_iss: true, algorithm: 'HS256' }) do |_headers, payload|
    secrets[payload['iss']]
  end
rescue JWT::InvalidIssuerError
  # Handle invalid token, e.g. logout user or deny access
end
```

### Required Claims

You can specify claims that must be present for decoding to be successful. JWT::MissingRequiredClaim will be raised if any are missing
```ruby
# Will raise a JWT::MissingRequiredClaim error if the 'exp' claim is absent
JWT.decode token, hmac_secret, true, { required_claims: ['exp'], algorithm: 'HS256' }
```

### X.509 certificates in x5c header

A JWT signature can be verified using certificate(s) given in the `x5c` header. Before doing that, the trustworthiness of these certificate(s) must be established. This is done in accordance with RFC 5280 which (among other things) verifies the certificate(s) are issued by a trusted root certificate, the timestamps are valid, and none of the certificate(s) are revoked (i.e. being present in the root certificate's Certificate Revocation List).

```ruby
root_certificates = [] # trusted `OpenSSL::X509::Certificate` objects
crl_uris = root_certificates.map(&:crl_uris)
crls = crl_uris.map do |uri|
  # look up cached CRL by `uri` and return it if found, otherwise continue
  crl = Net::HTTP.get(uri)
  crl = OpenSSL::X509::CRL.new(crl)
  # cache `crl` using `uri` as the key, expiry set to `crl.next_update` timestamp
end

begin
  JWT.decode(token, nil, true, { x5c: { root_certificates: root_certificates, crls: crls } })
rescue JWT::DecodeError
  # Handle error, e.g. x5c header certificate revoked or expired
end
```

### JSON Web Key (JWK)

JWK is a JSON structure representing a cryptographic key. This gem currently supports RSA, EC, OKP and HMAC keys. OKP support requires [RbNaCl](https://github.com/RubyCrypto/rbnacl) and currently only supports the Ed25519 curve.

To encode a JWT using your JWK:

```ruby
optional_parameters = { kid: 'my-kid', use: 'sig', alg: 'RS512' }
jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048), optional_parameters)

# Encoding
payload = { data: 'data' }
token = JWT.encode(payload, jwk.signing_key, jwk[:alg], kid: jwk[:kid])

# JSON Web Key Set for advertising your signing keys
jwks_hash = JWT::JWK::Set.new(jwk).export
```

To decode a JWT using a trusted entity's JSON Web Key Set (JWKS):

```ruby
jwks = JWT::JWK::Set.new(jwks_hash)
jwks.filter! {|key| key[:use] == 'sig' } # Signing keys only!
algorithms = jwks.map { |key| key[:alg] }.compact.uniq
JWT.decode(token, nil, true, algorithms: algorithms, jwks: jwks)
```


The `jwks` option can also be given as a lambda that evaluates every time a kid is resolved.
This can be used to implement caching of remotely fetched JWK Sets.

If the requested `kid` is not found from the given set the loader will be called a second time with the `kid_not_found` option set to `true`.
The application can choose to implement some kind of JWK cache invalidation or other mechanism to handle such cases.

Tokens without a specified `kid` are rejected by default.
This behaviour may be overwritten by setting the `allow_nil_kid` option for `decode` to `true`.

```ruby
jwks_loader = ->(options) do
  # The jwk loader would fetch the set of JWKs from a trusted source.
  # To avoid malicious requests triggering cache invalidations there needs to be
  # some kind of grace time or other logic for determining the validity of the invalidation.
  # This example only allows cache invalidations every 5 minutes.
  if options[:kid_not_found] && @cache_last_update < Time.now.to_i - 300
    logger.info("Invalidating JWK cache. #{options[:kid]} not found from previous cache")
    @cached_keys = nil
  end
  @cached_keys ||= begin
    @cache_last_update = Time.now.to_i
    # Replace with your own JWKS fetching routine
    jwks = JWT::JWK::Set.new(jwks_hash)
    jwks.select! { |key| key[:use] == 'sig' } # Signing Keys only
    jwks
  end
end

begin
  JWT.decode(token, nil, true, { algorithms: ['RS512'], jwks: jwks_loader })
rescue JWT::JWKError
  # Handle problems with the provided JWKs
rescue JWT::DecodeError
  # Handle other decode related issues e.g. no kid in header, no matching public key found etc.
end
```

### Importing and exporting JSON Web Keys

The ::JWT::JWK class can be used to import both JSON Web Keys and OpenSSL keys
and export to either format with and without the private key included.

To include the private key in the export pass the `include_private` parameter to the export method.

```ruby
# Import a JWK Hash (showing an HMAC example)
jwk = JWT::JWK.new({ kty: 'oct', k: 'my-secret', kid: 'my-kid' })

# Import an OpenSSL key
# You can optionally add descriptive parameters to the JWK
desc_params = { kid: 'my-kid', use: 'sig' }
jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048), desc_params)

# Export as JWK Hash (public key only by default)
jwk_hash = jwk.export
jwk_hash_with_private_key = jwk.export(include_private: true)

# Export as OpenSSL key
public_key = jwk.verify_key
private_key = jwk.signing_key if jwk.private?

# You can also import and export entire JSON Web Key Sets
jwks_hash = { keys: [{ kty: 'oct', k: 'my-secret', kid: 'my-kid' }] }
jwks = JWT::JWK::Set.new(jwks_hash)
jwks_hash = jwks.export
```

### Key ID (kid) and JWKs

The key id (kid) generation in the gem is a custom algorithm and not based on any standards.
To use a standardized JWK thumbprint (RFC 7638) as the kid for JWKs a generator type can be specified in the global configuration
or can be given to the JWK instance on initialization.

```ruby
JWT.configuration.jwk.kid_generator_type = :rfc7638_thumbprint
# OR
JWT.configuration.jwk.kid_generator = ::JWT::JWK::Thumbprint
# OR
jwk = JWT::JWK.new(OpenSSL::PKey::RSA.new(2048), nil, kid_generator: ::JWT::JWK::Thumbprint)

jwk_hash = jwk.export

thumbprint_as_the_kid = jwk_hash[:kid]
```

# Development and Tests

We depend on [Bundler](http://rubygems.org/gems/bundler) for defining gemspec and performing releases to rubygems.org, which can be done with

```bash
rake release
```

The tests are written with rspec. [Appraisal](https://github.com/thoughtbot/appraisal) is used to ensure compatibility with 3rd party dependencies providing cryptographic features.

```bash
bundle install
bundle exec appraisal rake test
```

## How to contribute
See [CONTRIBUTING](CONTRIBUTING.md).

## Contributors

See [AUTHORS](AUTHORS).

## License

See [LICENSE](LICENSE).
