Unable to use custom authorizer in API Gateway

Question

I have a couple of days trying to secure my API Gateway using custom authorizers with the auth0 service. I have my lambda which validates my bearer token, the Lambda does work if I invoke it inside the AWS console and when I create a custom authorizer I can successfully tested with a Bearer token.

When I try to attach the authorizer to my API Gateway methods and test the request with postman and the token provided by auth0 it always returns a 401 status code. I read my logs in CloudWatch and the authorization Lambda it's never triggered whenever I make the HTTP request. I am following this tutorial: https://auth0.com/docs/integrations/aws-api-gateway/custom-authorizers/

And this is my Authorization lambda code:

Handler:

'use strict';

let jwtManager = require("./jwt_manager");

module.exports.authenticate = (event, context, callback) => {

  jwtManager.validate(event, function (error, data) {
    if (error) {
      if (!error) {
        context.fail("Unhandled error");
      }
      context.fail(error);
    }
    else {
      console.log("SUCCEED");
      context.succeed(data);
    }
  });

};

And this is the jwtManager:

"use strict";
require("dotenv").config({ silent: true });

let jwksClient = require("jwks-rsa");
let jwt = require("jsonwebtoken");

module.exports.validate = function(params, callback) {
  var token = validateParams(params);

  var client = jwksClient({
    cache: true,
    rateLimit: true,
    jwksRequestsPerMinute: 10,
    jwksUri: process.env.JWKS_URI
  });

  var decodedJwt = jwt.decode(token, { complete: true });
  var kid = decodedJwt.header.kid;

  client.getSigningKey(kid, function(error, data) {
    if (error) {
        console.log(error);
      callback(error);
    } else {
      var signingKey = data.publicKey || data.rsaPublicKey;
      jwt.verify(
        token,
        signingKey,
        { audience: process.env.AUDIENCE, issuer: process.env.ISSUER },
        function(error, decoded) {
            if (error) {
                console.log("ERROR");
                console.log(error);
                callback(error);
            }
            else {
                console.log(decoded);
                var response = {
                    principalId: decoded.sub,
                    policyDocument: getPolicyDocument("Allow", params.methodArn),
                    context: {
                        scope: decoded.scope
                    }
                }
                console.log(response);
                console.log(response.policyDocument);
                callback(null, response);
            }
        }
      );
    }
  });
};

function validateParams(params) {
  var token;

  if (!params.type || params.type !== "TOKEN") {
    throw new Error("Expected 'event.type' parameter to have value TOKEN");
  }

  var tokenString = params.authorizationToken;
  if (!tokenString) {
    throw new Error("Expected 'event.authorizationToken' parameter to be set");
  }

  var match = tokenString.match(/^Bearer (.*)$/);
  if (!match || match.length < 2) {
    throw new Error(
      "Invalid Authorization token - '" +
        tokenString +
        "' does not match 'Bearer .*'"
    );
  }

  return match[1];
}

 function getPolicyDocument(effect, resource) {

    var policyDocument = {};
    policyDocument.Version = '2012-10-17'; // default version
    policyDocument.Statement = [];
    var statementOne = {};
    statementOne.Action = [ 'execute-api:Invoke', 'lambda:Invoke'] ; // default action
    statementOne.Effect = effect;
    statementOne.Resource = resource.split('/')[0] + '/*';
    policyDocument.Statement[0] = statementOne;
    return policyDocument;
}

Thanks in advance!

Answer 1

When you test an API Gateway with a custom authorizer attached but the auth lambda function never triggered, it is likely due to unsuccessful validation in token header name/ token pattern validation.

I am able to reproduce your issue.

The authorizer can only be triggered IF I change the header name from "Authorization" to "AuthorizationToken" in POSTMAN.

check the token header name I made the authorizer works

I think it is likely a new bug in AWS portal as I noticed they have changed the UI to configure API Gateway Authorizers not long ago.

It is very strange a HTTP request has to send bearer token in a header with name "AuthorizationToken". If your AWS plan allows you to access their technical support, you should alert them about this issue.