FirebaseAwsCustomAuth

AWS API Gateway Custom Authorizer for Firebase Auth tokens with .NET Core 2.0 backend.

AWS API Gateway Custom Authorizer for Firebase Auth

This project includes a sample custom authorizer Lambda application and test project for AWS API Gateway that uses Firebase Auth tokens. You can use Firebase Auth tokens to authenticate and authorize your Firebase users to your AWS API's.

JoeDM09 is the developer of custom authorizer for .NET Core, so thanks him for his work! Checkout his original pull request here.

Usage

1. To run the Lambda application, you need just your Firebase project id which you can get from your Firebase console.

using Amazon.Lambda.Core;
using Lambda.Models;
using Lambda.Models.Auth;
using Newtonsoft.Json;
using System;

// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.
[assembly: LambdaSerializer(typeof(Amazon.Lambda.Serialization.Json.JsonSerializer))]

namespace Lambda
{
    public class Function
    {
        public const string ProjectId = "YOUR_FIREBASE_PROJECT_ID_HERE";
        private JwtValidator JwtService { get; } = new JwtValidator();

        /// <summary>
        /// A simple function that takes the token authorizer and returns a policy based on the authentication token included.
        /// </summary>
        /// <param name="input">token authorization received by api-gateway event sources</param>
        /// <param name="context"></param>
        /// <returns>IAM Auth Policy</returns>
        [LambdaSerializer(typeof(Amazon.Lambda.Serialization.Json.JsonSerializer))]
        public AuthPolicy FunctionHandler(TokenAuthorizerContext input, ILambdaContext context)
        {
            try
            {
                context.Logger.LogLine($"{nameof(input.AuthorizationToken)}: {input.AuthorizationToken}");
                context.Logger.LogLine($"{nameof(input.MethodArn)}: {input.MethodArn}");

                // validate the incoming token
                // and produce the principal user identifier associated with the token

                // this could be accomplished in a number of ways:
                // 1. Call out to OAuth provider
                // 2. Decode a JWT token inline
                // 3. Lookup in a self-managed DB
                var result = JwtService.Validate(input.AuthorizationToken, ProjectId);
                if (!result.IsValid)
                {
                    throw new Exception(result.ErrorMesage);
                }
                var principalId = result.Token.Payload.Sub;
                context.Logger.LogLine($"sub: {principalId} is validated.");

                // you can send a 401 Unauthorized response to the client by failing like so:
                // throw new Exception("Unauthorized");

                // if the token is valid, a policy must be generated which will allow or deny access to the client

                // if access is denied, the client will receive a 403 Access Denied response
                // if access is allowed, API Gateway will proceed with the backend integration configured on the method that was called

                // build apiOptions for the AuthPolicy
                var methodArn = ApiGatewayArn.Parse(input.MethodArn);
                var apiOptions = new ApiOptions(methodArn.Region, methodArn.RestApiId, methodArn.Stage);

                // this function must generate a policy that is associated with the recognized principal user identifier.
                // depending on your use case, you might store policies in a DB, or generate them on the fly

                // keep in mind, the policy is cached for 5 minutes by default (TTL is configurable in the authorizer)
                // and will apply to subsequent calls to any method/resource in the RestApi
                // made with the same token

                // the example policy below denies access to all resources in the RestApi
                var policyBuilder = new AuthPolicyBuilder(principalId, methodArn.AwsAccountId, apiOptions);
                policyBuilder.AllowAllMethods();
                // policyBuilder.AllowMethod(HttpVerb.GET, "/users/username");

                // finally, build the policy
                var authResponse = policyBuilder.Build();

                //// new! -- add additional key-value pairs
                //// these are made available by APIGW like so: $context.authorizer.<key>
                //// additional context is cached
                //authResponse.Context.Add("key", "value"); // $context.authorizer.key -> value
                //authResponse.Context.Add("number", 1);
                //authResponse.Context.Add("bool", true);

                return authResponse;
            }
            catch (Exception ex)
            {
                context.Logger.LogLine($"Exception caught: {JsonConvert.SerializeObject(ex)}");
                throw ex;
            }
        }
    }
}

2. To run integration tests, you need your Firebase project id and a valid/invalid token from your Firebase project.

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Xunit;

namespace Lambda.Tests
{
    public sealed class JwtValidatorIntegrationTests
    {
        private const string TOKEN = "YOUR_FIREBASE_JWT_TOKEN_HERE";
        private const string PROJECT_ID = "YOUR_FIREBASE_PROJECT_ID_HERE";

        [Theory]
        [InlineData(TOKEN, PROJECT_ID)]
        public void CanValidateValidToken(string token, string projectId)
        {
            var validator = new JwtValidator();
            var result = validator.Validate(token, projectId);

            Assert.True(result.IsValid, result.ErrorMesage);
            Assert.NotNull(result.Token);
        }

        [Theory]
        [InlineData(TOKEN, PROJECT_ID)]
        public void PerformanceTestValidation(string token, string projectId)
        {
            var tasks = new List<Task>();
            for (var i = 0; i < Environment.ProcessorCount; i++)
            {
                tasks.Add(Task.Run(() => RunValidationFor(1000, token, projectId)));
            }

            Task.WaitAll(tasks.ToArray());
        }

        private void RunValidationFor(int count, string token, string projectId)
        {
            var validator = new JwtValidator();
            for (var i = 0; i < count; i++)
            {
                validator.Validate(token, projectId);
            }
        }
    }
}