Introduction
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Our identities shape who we are, both personally and professionally. Just as I rely on my employee badge to access the office or my passport for international travel, the same principle applies to cloud applications and APIs. To establish secure access for application users, we need to define who can utilize the application resources and the extent of that access. This is achieved through identity controls that verify authentication (AuthN) and authorization (AuthZ), which—though related—are distinct concepts.
Amazon Cognito offers powerful tools for building, securing, and scaling user management and authentication solutions across platforms and devices. In this article, we’ll explore how to leverage Amazon Cognito to authenticate API calls to Amazon API Gateway, thereby securing access to your API resources.
Understanding Amazon Cognito
Amazon Cognito comprises three main services:
- Amazon Cognito Federated Identities
- Amazon Cognito User Pools
- Amazon Cognito Sync
This post will focus on the first two services, which can function independently or be configured to work together.
Amazon Cognito Federated Identities
To integrate Amazon Cognito Federated Identities into your application, you must create an identity pool—a repository of user data specific to your account. This pool can be set up to require an identity provider (IdP) for user authentication, with relevant app IDs or keys inputted.
Once validated, the IdP sends an identity token to Amazon Cognito Federated Identities, which then contacts the AWS Security Token Service (AWS STS) to obtain temporary AWS credentials linked to the authenticated IAM role associated with the identity pool. This role includes appropriate IAM policies that enable access to various AWS services.
In essence, Amazon Cognito Federated Identities can be likened to a token vending machine utilizing STS as its backend. The simplified user authentication flow is as follows:
- The app sends user credentials (typically username and password) to the IdP.
- Upon successful authentication, the IdP returns a valid token to the application.
- The app forwards this token to its associated identity pool.
- Amazon Cognito Federated Identities verifies the token with the IdP.
- If the token is valid, it contacts STS to acquire temporary access credentials (access key, secret key, and session token) based on the authenticated IAM role.
- The app uses these temporary credentials to access specific AWS services.
For those who don’t utilize an IdP, Amazon Cognito Federated Identities can support unauthenticated identities by providing a unique identifier and AWS credentials for users without an IdP login. If your application allows guest users, this feature can be enabled. In such scenarios, STS will issue temporary credentials based on a specific unauthenticated IAM role with suitable policies. It is crucial to adhere to the principle of least privilege, ensuring users can only perform necessary tasks.
Amazon Cognito User Pools
Conversely, Amazon Cognito User Pools serve as a comprehensive IdP that enables you to maintain a user directory and facilitate sign-up and sign-in for your web or mobile application. Utilizing JSON Web Tokens (JWTs) for user authentication and validation, JWTs are compact, digitally signed representations that securely transmit information between parties.
User Pools and identity pools can be combined to provide seamless access to your application. A user authenticated through a User Pool with a username and password can send a JWT to an associated identity pool, which will then return temporary AWS credentials to access other AWS services.
Think of Amazon Cognito User Pools as providing you with a passport (JWT) that allows you to obtain a boarding pass (access credentials) from an identity pool. This boarding pass permits you to proceed to the airport gate and board your flight to the AWS Cloud—a fitting analogy. The boarding pass is time-sensitive, just as the token (passport) authenticates the user and the temporary credentials (boarding pass) authorize access.
A Practical Example – Integrating Amazon Cognito with API Gateway
To illustrate the potential of Amazon Cognito User Pools and Federated Identities for authorizing access to your API Gateway API, consider a simple AngularV4 single-page web application.
This sample application authenticates users with three different IdPs and interfaces with an API Gateway API, which features three distinct resources (paths)—one for each user type. Each provider is restricted to its specific API resource/path, preventing access to others.
After authentication, the user retrieves attributes like first name, last name, and email from their provider and sends a POST request to the API resource with this data. Upon successful access, an AWS Lambda function is triggered to add the user’s details to an Amazon DynamoDB table.
This example utilizes a single identity pool and a single API Gateway API to showcase secure API access using multiple providers, various AuthN/AuthZ options, while sharing the same resources.
Both the “/google” and “/cip” resources are configured with IAM authorization for their GET/POST methods, whereas methods in “/cup” are secured using a user pool authorizer.
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Conclusion
In summary, integrating Amazon Cognito Federated Identities and User Pools with Amazon API Gateway can enhance the security of your APIs while providing a flexible user experience. As organizations grow, establishing secure access controls becomes increasingly critical for protecting sensitive data and resources.
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