API Gateway Authorizers
Implement various API Gateway authorizers, including Lambda custom authorizers and JWT authorizers, for robust authentication.
API Gateway Authorizers is a free Serverless Backend with AWS Lambda & API Gateway lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Serverless Backend with AWS Lambda & API Gateway learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
API Gateway Authorizers Intro
Welcome! In this lesson, we'll learn how to secure your serverless APIs using API Gateway Authorizers. These are crucial for controlling who can access your backend services.
Think of an authorizer as a security guard at the entrance of your API. Before any request reaches your Lambda function or other backend service, the authorizer checks the request's credentials.
Why Use API Gateway Authorizers?
Authorizers provide robust authentication and authorization for your APIs. Here's why they are essential:
- Protect Backend Resources: Prevent unauthorized access to your Lambda functions and other services.
- Decouple Auth Logic: Separate authentication logic from your main business logic, keeping your functions cleaner.
- Fine-Grained Access: Control access to specific API methods or resources based on user identity or roles.
Types of Authorizers
API Gateway offers several types of authorizers. Today, we'll focus on the two most flexible and commonly used:
- Lambda Custom Authorizers: A Lambda function you write to perform custom authentication.
- JWT Authorizers: API Gateway's native support for validating JSON Web Tokens (JWTs).
There's also IAM Authorizers, which use AWS IAM roles and policies, but we'll focus on the custom and JWT types here.
Lambda Custom Authorizers Explained
A Lambda Custom Authorizer is a Lambda function that you provide. API Gateway invokes this function with the incoming request's authorization token (e.g., from the Authorization header).
Your Lambda function then processes this token, performs its custom authentication logic (e.g., checks a database, calls an identity provider), and returns an IAM policy.
The Authorization Policy
The core output of your Lambda authorizer is an IAM policy document. This policy tells API Gateway whether to Allow or Deny the request to the target API endpoint.
It includes a principalId (the authenticated user's identifier) and a policyDocument specifying the permissions. If Allow, the request proceeds; if Deny, it's rejected with a 401 Unauthorized error.
Lambda Authorizer Code Example
Here's a simple Python Lambda function acting as an authorizer. It checks for a specific token and returns an 'Allow' or 'Deny' policy based on it.
Try changing the token in the test event to see different outputs!
def lambda_handler(event, context):
token = event.get('authorizationToken')
method_arn = event.get('methodArn')
if token == "my-secret-token-123":
# Allow access
return {
"principalId": "user123",
"policyDocument": {
"Version": "2012-10-17",
"Statement": [
{
"Action": "execute-api:Invoke",
"Effect": "Allow",
"Resource": method_arn
}
]
}
}
else:
# Deny access
return {
"principalId": "anonymous",
"policyDocument": {
"Version": "2012-10-17",
"Statement": [
{
"Action": "execute-api:Invoke",
"Effect": "Deny",
"Resource": method_arn
}
]
}
}
# --- Local Test (for demonstration) ---
if __name__ == "__main__":
print("Testing with 'my-secret-token-123':")
event_allow = {
"authorizationToken": "my-secret-token-123",
"methodArn": "arn:aws:execute-api:us-east-1:123456789012:/test/GET/items"
}
print(lambda_handler(event_allow, None))
print("\nTesting with 'invalid-token':")
event_deny = {
"authorizationToken": "invalid-token",
"methodArn": "arn:aws:execute-api:us-east-1:123456789012:/test/GET/items"
}
print(lambda_handler(event_deny, None))JWT Authorizers Explained
JWT (JSON Web Token) Authorizers allow API Gateway to natively validate JWTs. Instead of writing a Lambda function, you configure API Gateway with details about your JWT issuer.
When a request with a JWT comes in, API Gateway automatically performs validation steps like:
- Signature verification
- Expiration checks
- Audience and issuer validation
Configuring a JWT Authorizer
To set up a JWT authorizer, you typically provide API Gateway with:
- Issuer URL: The URL of the identity provider (e.g.,
https://cognito-idp.us-east-1.amazonaws.com/us-east-1_XXXXXXXfor Cognito). - Audience(s): A list of valid audiences for the token, ensuring the token is intended for your API.
- Identity Source: The header where the JWT is expected (e.g.,
$request.header.Authorization).
API Gateway then uses these details to fetch public keys and validate incoming JWTs.
When to Use Which Authorizer?
Choosing between Lambda and JWT authorizers depends on your needs:
- Lambda Authorizer: Use for highly custom authentication logic, integration with legacy systems, or identity providers not supporting standard OIDC/OAuth2. Offers maximum flexibility.
- JWT Authorizer: Ideal when using standard identity providers like AWS Cognito User Pools, Auth0, Okta, etc. It's simpler to set up and has less operational overhead.
For most modern applications using standard identity providers, JWT authorizers are often the preferred choice.
Authorizer Quick Check
Time for a quick check on what you've learned about API Gateway Authorizers!
Recap: Securing with Authorizers
You've now learned about API Gateway Authorizers, a vital component for securing your serverless APIs!
- Authorizers act as a front-door security check for your API endpoints.
- Lambda Custom Authorizers offer maximum flexibility for custom authentication logic.
- JWT Authorizers provide native, easy-to-configure validation for standard JSON Web Tokens.
By implementing authorizers, you ensure only legitimate requests access your backend services, enhancing the security of your applications.
Frequently asked questions
Is the “API Gateway Authorizers” lesson free?
Yes — the full text of “API Gateway Authorizers” is free to read here on the web, and the Serverless Backend with AWS Lambda & API Gateway course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Serverless Backend with AWS Lambda & API Gateway course, upgrade to CoddyKit PRO.
What will I learn in “API Gateway Authorizers”?
Implement various API Gateway authorizers, including Lambda custom authorizers and JWT authorizers, for robust authentication. You practise Serverless Backend with AWS Lambda & API Gateway with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Serverless Backend with AWS Lambda & API Gateway?
No prior experience is required. Serverless Backend with AWS Lambda & API Gateway on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “API Gateway Authorizers” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Serverless Backend with AWS Lambda & API Gateway lesson?
Yes. Every Serverless Backend with AWS Lambda & API Gateway lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- IAM Roles and Permissions
- API Gateway Authorizers
- Securing Lambda with VPC
- Protecting Secrets with AWS Secrets Manager