Troubleshooting JWT validation

When a client application includes a JSON Web Token (JWT) in a request to an API, the Extensible Service Proxy (ESP) validates the JWT before sending the request to the API backend. This page provides troubleshooting information if the JWT validation fails and ESP returns an error in the response to the client. See RFC 7519 for more information about JWTs.

Error: BAD_FORMAT

Check the following:

  • Make sure the JWT contains valid JSON.
  • Check that the JWT header has the "alg" field and is set to one of the following: "RS256", "HS256", "RS384", "HS384", "RS512", or "HS512"
  • Check the data type of the following fields (if they are present) in the JWT payload:
    • The "iat" (issued at), "exp" (expiration time), and "nbf"(not before) claims are numbers greater than 0 and not strings.
    • The "sub" (subject), "iss" (issuer), and "jti" (JWT ID) fields are strings.
    • The "aud" (audience) claim is either a string or an array of strings.
  • Ensure that the following claims are present in the JWT payload: "sub" (subject), "iss" (issuer), and "aud" (audience).

The following is an example of a decoded JWT token that is valid:

{
  "alg": "RS256",
  "typ": "JWT",
  "kid": "42ba1e234ac91ffca687a5b5b3d0ca2d7ce0fc0a"
}

Payload:
{
  "iss": "myservice@myproject.iam.gserviceaccount.com",
  "iat": 1493833746,
  "aud": "myservice.appspot.com",
  "exp": 1493837346,
  "sub": "myservice@myproject.iam.gserviceaccount.com"
}
Error: TIME_CONSTRAINT_FAILURE

Use jwt.io to decode the JWT and make sure that:

  • The "exp" (expiration time) claim exists.
  • The "exp" (expiration time) claim value is a date and time in the future. The current date and time must be before the expiration date and time listed in the "exp" claim.
  • The "nbf" (not before) claim (If present) is a date and time in the past. The current date and time must be after or equal to the date and time listed in the "nbf" claim.
Error: UNKNOWN

Use jwt.io to decode the JWT and ensure that:

  • If the "iss" (issuer) claim is an email address, then the "sub" (subject) and "iss" claims should be the same. This is to ensure that for e-mail issuers, the JWT is self issued.

Error: KEY_RETRIEVAL_ERROR

  • Check that the public key URI specified in the jwks_uri field in the authentication: providers section of your gRPC .yaml configuration file is correct and valid.

Error: Issuer not allowed

  • Check that the "iss" (issuer) claim in your JWT token matches the issuer field in the authentication: providers section of your gRPC .yaml configuration file.

Error: Audience not allowed

If the "aud" (audience) claim in a JWT token matches the Endpoints service name, then the ESP validates the audience and ignores the audiences values in your gRPC .yaml configuration file. For example, if your service name is "myservice.endpoints.example-project-12345.cloud.goog", then a JWT with "aud" set to "myservice.endpoints.example-project-12345.cloud.goog" or "https://myservice.endpoints.example-project-12345.cloud.goog" is a valid audience.

If the "aud" claim isn't the same as the Endpoints service name:

  • Check that the "aud" claim in the JWT matches one of the audiences values specified in the authentication: providers section of your gRPC .yaml configuration file.
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