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API Gateway Emulator

It is a very simple gateway server that mimics the behavior of Google Cloud API Gateway.

This gateway is not intended for full emulation. The following is a task list.

  • Read the authorization header of the request to check for authentication.
    • Unlike the real Gateway, the authentication settings are read from environment variables.
  • Set the Base64URL-encoded authenticated user information in the x-apigateway-api-userinfo request header.
  • Copy the value of the authorization header into the request header x-forwarded-authorization.
    • Since the authorization is not rewritten like in the real API Gateway, it is passed to the target API with the same value set.
  • Forwards the request with the header added to the target URL and returns the received response.
    • Unlike the actual Gateway, the target URL is read from an environment variable. Also, it cannot be specified individually for each path.

It is intended to be used when developing in a local environment. Please use the real thing in a production environment.

Usage

This is an example of authenticating with Auth0 and accessing the API on localhost:5050.

yarn

# Build
yarn build

# Run
TARGET_URL="http://localhost:5050" \
OAUTH_JWKS_URI="https://YOUR_AUTH0_TENANT_DOMAIN/.well-known/jwks.json" \
OAUTH_ISSUER="https://YOUR_AUTH0_TENANT_DOMAIN/" \
OAUTH_AUDIENCE="YOUR_AUTH0_API_AUDIENCE" \
yarn start

# Request target API resource via Gateway
curl --request GET \
  --url "http://localhost:3000/api/users/xxxx" \
  --header 'authorization: Bearer YOUR_ACCESS_TOKEN'

By creating an .env file in the project root, you don't need to specify environment variables when executing commands.

Docker

docker pull fuji44/api-gateway-emulator

# Run
docker run -it --rm -p 3000:3000 \
  -e TARGET_URL="http://host.docker.internal:5050" \
  -e OAUTH_JWKS_URI="https://YOUR_AUTH0_TENANT_DOMAIN/.well-known/jwks.json" \
  -e OAUTH_ISSUER="https://YOUR_AUTH0_TENANT_DOMAIN/" \
  -e OAUTH_AUDIENCE="YOUR_AUTH0_API_AUDIENCE" \
  fuji44/api-gateway-emulator

# Request target API resource via Gateway
curl --request GET \
  --url "http://localhost:3000/api/users/xxxx" \
  --header 'authorization: Bearer YOUR_ACCESS_TOKEN'

It is also a good idea to use the --env-file option to easily specify environment variables.

Configuration

The behavior can be changed by specifying the following environment variables. The authentication behavior changes depending on the AUTH_TYPE. The options to be specified are also different, so please check them carefully.

# Require: Target API URL
TARGET_URL=http://localhost:5050
# Option: Target Base Path
BASE_PATH=/
# Option: Listen port
PORT=3000
# Option: Verbose log output
VERBOSE=true

# Specify the authentication method
# jwks (default) or dummy_jwt
AUTH_TYPE=dummy_jwt

JWKS Type Config

If jwks is specified, the user information confirmed by the actual JWKS will be set in the header.

# jwks type configs
# e.g. Auth0
OAUTH_JWKS_URI=https://YOUR_AUTH0_TENANT_DOMAIN/.well-known/jwks.json
OAUTH_ISSUER=https://YOUR_AUTH0_TENANT_DOMAIN/
OAUTH_AUDIENCE=YOUR_AUTH0_API_AUDIENCE
# Option: comma-separated signing algorithms
OAUTH_TOKEN_SIGN_ALGORITHMS=RS256

Dummy JWT Type Config

If dummy_jwt is specified, no authentication is performed and the content of dummy JSON is set in the header. The Gateway doesn't care what's in the JSON, but normally you would expect the backend API to be JWT Claims.

# dummy_jwt type configs
DUMMY_JWT_JSON=./dummy-jwt.json

JWT Claims Sample

{
  "iss": "https://example.com/",
  "sub": "dummy@example.com",
  "aud": "https://example.com/",
  "iat": 1645496234,
  "exp": 1645582634,
  "azp": "dummy",
  "gty": "dummy"
}

In order to pass JSON to the container, you need to mount the volume by specifying -v or something similar.

docker run -it --rm -p 3000:3000 \
  -v $(pwd)/temp:/usr/local/api-gateway/temp \
  -e TARGET_URL="http://host.docker.internal:5050" \
  -e AUTH_TYPE="dummy_jwt" \
  -e DUMMY_JWT_JSON="/usr/local/api-gateway/temp/dummy-jwt.json" \
  fuji44/api-gateway-emulator

License

The MIT License.

Copyright (c) 2021 Yoshihiro Fujimoto