JWT Validation

Document updated on May 23, 2023

Protect endpoints from public usage by validating JWT tokens generated by any industry-standard OpenID Connect (OIDC) integration.

Before digging any further, here are some answers to frequently asked questions:

1. KrakenD does not generate the tokens itself. Still, you can plug it into any SaaS or self-hosted OpenID Identity Provider (IdP) using industry standards (e.g., Auth0, Azure AD, Google Firebase, Keycloak, etc.)

2. KrakenD does not need to validate all calls using your IdP. KrakenD validates every incoming call’s signature and it doesn’t make token introspection (asking for the IdP data about the token owner).

3. If you don’t have an identity server, you can still use your classic monolith/backend login system and adapt it to return a JWT payload (a simple JSON). From here, let KrakenD sign the token for you and start using tokens immediately.

4. Your self-hosted identity server doesn’t need to be exposed to the Internet, as it can live behind KrakenD and let the token generation requests be proxied through KrakenD.

5. I have tokens generated by the provider XYZ, are they supported? Yes. We still need to find a single major provider that doesn’t follow the JSON Web Encryption (RFC 7516), JSON Web Signature (RFC 7515), or JSON Web Token (RFC 7519) specifications.

6. If you are new to JWT validation, start reading the JSON Web Tokens overview

JWT header requirements

When KrakenD decodes the base64 token string passed in the Bearer or a cookie, it expects to find in its header section the following fields:

{
    "alg": "RS256",
    "kid": "MDNGMjU2M0U3RERFQUEwOUUzQUMwQ0NBN0Y1RUY0OEIxNTRDM0IxMw"
}

The alg and kid values depend on your implementation, but they must be present.

The example above used this public key. Notice how the kid matches the single key present in the JWK document and the token header.

KrakenD is built with security in mind and uses JWS (instead of plain JWT or JWE), and the kid points to the right key in the JWS. This is why this entry is mandatory to validate your tokens.

Basic JWT validation

The JWT validation must be present inside every endpoint definition needing it. If several endpoints are going to require JWT validation, consider using the flexible configuration to avoid repetitive declarations.

Enable the JWT validation by adding the namespace "auth/validator" inside the extra_config of the desired endpoint. Do not forget to add caching.

For instance, to protect the endpoint /protected/resource:

{
    "endpoint": "/protected/resource",
    "extra_config": {
        "auth/validator": {
            "alg": "RS256",
            "audience": ["http://api.example.com"],
            "roles_key": "http://api.example.com/custom/roles",
            "roles": ["user", "admin"],
            "jwk_url": "https://albert-test.auth0.com/.well-known/jwks.json",
            "cache": true
        }
    },
    "backend": [
        {
        "url_pattern": "/"
        }
    ]
}

This configuration makes sure that:

• The signature of the token matches with the keys under the JWK URL
• The key from the identity server is cached to avoid hammering it
• The token is well-formed and didn’t expire
• The token has a valid signature
• The role of the user is either user or admin (taken from a key in the JWT payload named http://api.example.com/custom/roles)
• The token is not revoked in the bloom filter (see revoking tokens)

JWT validation settings

The following settings are available for JWT validation. There are many options, although generally only the fields alg and jwk_url or jwk_local_path are mandatory, and the rest of the keys can be added or not at your best convenience or depending on other options.

These options are for the extra_config’s namespace "auth/validator" placed in every endpoint (use flexible configuration to avoid code repetition):

Here there is an example using an external jwk_url:

{
    "endpoint": "/foo",
    "extra_config": {
        "auth/validator": {
            "alg": "RS256",
            "jwk_url": "https://url/to/jwks.json",
            "cache": true,
            "audience": [
                "audience1"
            ],
            "roles_key": "department",
            "roles_key_is_nested": false,
            "roles": [
                "sales",
                "development"
            ],
            "scopes_key": "my_scopes",
            "scopes_matcher": "any",
            "scopes": [
                "resource1:action1",
                "resource2:action1",
                "resource1:action2"
            ],
            "issuer": "http://my.api.com",
            "cookie_key": "TOKEN",
            "disable_jwk_security": true,
            "jwk_fingerprints": [
                "S3Jha2VuRCBpcyB0aGUgYmVzdCBnYXRld2F5LCBhbmQgeW91IGtub3cgaXQ=="
            ],
            "cipher_suites": [
                10, 47, 53
            ],
            "operation_debug": true
    }
}
}

Caching keys

A crucial decision when using JWT is defining a caching strategy that works with your key rotation policy.

If you don’t set any caching option, KrakenD will default to the more pessimistic scenario where you rotate the keys continuously, and KrakenD needs to download the keys in the JWK URL every single time. In most cases, this option will add a lot of pressure to your identity server. Therefore, we encourage you to enable cache in each endpoint, and even better if you add the second-level shared cache in the JWK client with shared_cache_duration. For instance:

{
    "version": 3,
    "extra_config": {
        "auth/jwk-client": {
            "@comment": "Enable a JWK shared cache amongst all endpoints of 15 minutes",
            "shared_cache_duration": 900
        }
    },
    "endpoints": [{
      "endpoint": "/protected",
      "extra_config": {
        "auth/validator": {
            "cache": true,
            "cache_duration": 3600,
            "@comment": "Rest of the validator options omitted for simplicity"
        }
      }
    }]
}

Read more about JWK caching

Validation process

KrakenD does the following validation to let users hit protected endpoints:

• The jwk_url must be accessible by KrakenD at all times (caching is recommended)
• The token is well formed
• The kid in the header is listed in the jwk_url or jwk_local_path.
• The content of the JWK Keys (k) is base64 urlencoded
• The algorithm alg is supported by KrakenD and matches exactly the one used in the endpoint definition.
• The token hasn’t expired
• The signature is valid.
• The given issuer matches (if present in the configuration), and is a string
• The given audience matches (if present in the configuration), and is a string
• The given claims are within the endpoint accepted roles (if present in the configuration))
• All numeric claims checking is represented as a float64 (decimal).

The configuration allows you to define the set of required roles. For example, a user who passes a token with roles A and B, can access an endpoint requiring "roles": ["A","C"] as it has one of the required options (A).

If the token is expired, the configuration inside the namespace is incorrect, the signature doesn’t match, the required claims do not match, or the token is revoked, a 401 Unauthorized is returned.

When the token doesn’t include the defined ACL’s required roles, a 403 Forbidden is returned.

When you generate tokens for end-users, make sure to set a low expiration. Tokens are supposed to have short lives and should expire in a few minutes or hours.

Accepted providers for encrypting payloads

When using a jwk_local_path, the secret_url scheme accepts different providers:

Local secrets

The local secrets require an URL with the following scheme:

base64key://base64UrlEncondedContent

The URL host must be base64 url encoded and must decode to exactly 32 bytes. Here is an example of the extra_config:

{
    "jwk_local_path":"./jwk.txt",
    "secret_url":"base64key://smGbjm71Nxd1Ig5FS0wj9SlbzAIrnolCz9bQQ6uAhl4=",
    "cypher_key":"gCERmfqHMoEu3+utqBa/R1oMZYIvh0OOKtJmnX/hDPDxbXCGXGvO3SF7B5FWxrJnRW7rnjGIV4eP2VLrYX2q9pJM49BpP+A9"
}

This config will use the key smGbjm71Nxd1Ig5FS0wj9SlbzAIrnolCz9bQQ6uAhl4= for decrypting de cypher_key (base64 standard enconded) and then decrypting the content of the file ./jwt.txt.

See this test to understand how to generate and encrypt payloads.

Amazon KMS

awskms://keyID

The URL Host + Path is used as the key ID, which can be an Amazon Resource Name (ARN), alias name, or alias ARN. Note that ARNs may contain “:” characters, which cannot be escaped in the Host part of a URL, so you should use the awskms:///<ARN> form.

More information about AWS KMS

Azure’s Key Vault

azurekeyvault://keyID

The credentials are taken from the environment unless the AZURE_KEYVAULT_AUTH_VIA_CLI environment variable is set to true, in which case it uses the az command line.

More information about Azure Key Vault

Google Cloud KMS

gcpkms://projects/[PROJECT_ID]/locations/[LOCATION]/keyRings/[KEY_RING]/cryptoKeys/[KEY]

You can take the URL from the GCP console.

Hashicorp’s Vault

hashivault://keyID

Environment variables VAULT_SERVER_URL and VAULT_SERVER_TOKEN are used.

Passing claims to the backend URL

Since KrakenD 1.2.0, it is possible to use data present in the claims to inject it into the backend’s final URL. The notation of the url_pattern field includes the parsing of {JWT.some_claim}, where some_claim is an attribute of your claim.

For instance, when your JWT payload is represented by something like this:

{
    "sub": "1234567890",
    "name": "Mr. KrakenD"
}

Having a backend defined with:

{
    "url_pattern": "/foo/{JWT.sub}",
    "method": "POST"
}

The call to your backend would produce the request:

POST /foo/1234567890

Keep in mind that this syntax in the url_pattern field is only available if the backend loads the extra_config "auth/validator" and that it does not work with nested attributes in the payload.

If KrakenD can’t replace the claim’s content for any reason, the backend receives a request to the literal URL /foo/{JWT.sub}.

Propagate JWT claims as request headers

It is possible to forward claims in a JWT as request headers. It is a common use case to have, for instance, the sub claim added as an X-User header to the request. The propagation makes that other KrakenD components, such as rate-limiting, can work with information in the token.

Important: The endpoint input_headers needs to be set as well, so the backend can see it.

{
    "extra_config": {
        "auth/validator": {
            "propagate_claims": [
                ["sub", "x-user"],
                ["realm_access.role", "x-role"]
            ]
        }
    }
}

In this case, the sub claim’s value will be added as x-user header to the request. If the claim does not exist, the mapping is just skipped.

In addition, the nested property role (inside realm_access) is passed as an x-role header.

A complete running example

The KrakenD Playground demonstrates how to protect endpoints using JWT and includes two examples ready to use:

• Integration with an external third party using a Single Page Application from Auth0
• Integration with an internal identity provider service (mocked) using a symmetric key algorithm and a signer middleware.

To try it, clone the playground and follow the README.

Supported hashing algorithms and cipher suites

Hashing algorithms

Accepted values for the alg field are:

• EdDSA: EdDSA
• HS256: HMAC using SHA-256
• HS384: HMAC using SHA-384
• HS512: HMAC using SHA-512
• RS256: RSASSA-PKCS-v1.5 using SHA-256
• RS384: RSASSA-PKCS-v1.5 using SHA-384
• RS512: RSASSA-PKCS-v1.5 using SHA-512
• ES256: ECDSA using P-256 and SHA-256
• ES384: ECDSA using P-384 and SHA-384
• ES512: ECDSA using P-521 and SHA-512
• PS256: RSASSA-PSS using SHA256 and MGF1-SHA256
• PS384: RSASSA-PSS using SHA384 and MGF1-SHA384
• PS512: RSASSA-PSS using SHA512 and MGF1-SHA512

Cipher suites

Accepted values for cipher suites are:

• 5: TLS_RSA_WITH_RC4_128_SHA
• 10: TLS_RSA_WITH_3DES_EDE_CBC_SHA
• 47: TLS_RSA_WITH_AES_128_CBC_SHA
• 53: TLS_RSA_WITH_AES_256_CBC_SHA
• 60: TLS_RSA_WITH_AES_128_CBC_SHA256
• 156: TLS_RSA_WITH_AES_128_GCM_SHA256
• 157: TLS_RSA_WITH_AES_256_GCM_SHA384
• 49159: TLS_ECDHE_ECDSA_WITH_RC4_128_SHA
• 49161: TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
• 49162: TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
• 49169: TLS_ECDHE_RSA_WITH_RC4_128_SHA
• 49170: TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA
• 49171: TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
• 49172: TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
• 49187: TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256
• 49191: TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256

Default suites are:

• 49199: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
• 49195: TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
• 49200: TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
• 49196: TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
• 52392: TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305
• 52393: TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305