Web Identity Federation vs Amazon Cognito: Which to Use for Mobile and Web Apps

Web Identity Federation vs Amazon Cognito: Which to Use for Mobile and Web Apps#

Building modern applications that serve millions of users means handling authentication and authorization at scale. If you’re building a mobile app or web application that needs to authenticate users through external providers like Google or Facebook—or even your own OIDC identity provider—you’ve likely encountered the concept of web identity federation. What you may not realize is that there are two fundamentally different approaches to implementing this, and choosing between them can significantly impact your application’s maintainability, security posture, and long-term scalability.

This article explores the distinction between raw web identity federation and Amazon Cognito Identity Pools, two approaches that often confuse developers because they solve related but distinctly different problems. We’ll walk through how each works, examine their respective strengths and limitations, and help you make an informed decision for your application.

Understanding the Core Problem Web Identity Federation Solves#

Before diving into the comparison, let’s establish what web identity federation actually addresses. Imagine you’re building a mobile app that authenticates users via Google. After a user successfully logs in with Google, you need a way to grant them AWS credentials—temporary credentials that allow them to call AWS services directly, like uploading files to an S3 bucket or writing data to DynamoDB. This is where web identity federation comes in.

The fundamental challenge is this: your users have credentials from Google (or Facebook, Apple, or your own identity provider), but AWS doesn’t natively understand those credentials. You need a mechanism to bridge that gap and issue temporary AWS credentials that correspond to the external identity. Web identity federation is AWS’s answer to this problem.

The Raw Web Identity Federation Approach#

Let’s start by understanding how raw web identity federation works at its simplest level. In this approach, your application directly exchanges tokens from an external identity provider for AWS credentials without using Cognito as an intermediary.

Here’s the typical flow: A user logs in with Google using the Google Sign-In SDK in your mobile app. Google returns an ID token to your app. Your app then directly calls the AWS Security Token Service (STS) using the AssumeRoleWithWebIdentity API, passing the Google ID token. If the token is valid and properly configured, AWS returns temporary security credentials (access key, secret key, and session token). Your app can now use these credentials to make direct calls to AWS services.

To implement this, you’d first need to set up a trust relationship on an IAM role. This role would trust the external identity provider—in this case, Google. Here’s what that trust policy looks like:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Federated": "accounts.google.com"
      },
      "Action": "sts:AssumeRoleWithWebIdentity",
      "Condition": {
        "StringEquals": {
          "accounts.google.com:aud": "YOUR_GOOGLE_CLIENT_ID"
        }
      }
    }
  ]
}

From your application’s perspective, the code is straightforward. Using the AWS SDK, you’d do something like this:

import { STSClient, AssumeRoleWithWebIdentityCommand } from "@aws-sdk/client-sts";

const stsClient = new STSClient({ region: "us-east-1" });

async function getAwsCredentialsFromGoogle(googleIdToken) {
  const command = new AssumeRoleWithWebIdentityCommand({
    RoleArn: "arn:aws:iam::123456789012:role/GoogleFederatedRole",
    RoleSessionName: "google-session",
    WebIdentityToken: googleIdToken,
    DurationSeconds: 3600
  });

  const response = await stsClient.send(command);
  return {
    accessKeyId: response.Credentials.AccessKeyId,
    secretAccessKey: response.Credentials.SecretAccessKey,
    sessionToken: response.Credentials.SessionToken,
    expiration: response.Credentials.Expiration
  };
}

This approach has a certain elegance to it—it’s direct and cuts out the middleman. However, as your application grows in complexity, several limitations emerge.

Limitations of Raw Web Identity Federation#

The first limitation is token refresh complexity. ID tokens from identity providers like Google are typically short-lived, often valid for just one hour. When your token expires, you need to refresh it through the identity provider, then exchange the new token for new AWS credentials. This means your application logic needs to handle multiple levels of token management and refresh timing. You’re essentially managing two separate token lifecycles, and coordinating them becomes increasingly error-prone.

The second limitation is inability to unify multiple identity providers. If you want to support users logging in through Google, Facebook, and Apple simultaneously, raw web identity federation requires you to create separate IAM roles for each provider. Your backend logic must then map users to the correct role based on which provider they used. This might seem manageable with three providers, but imagine supporting ten or more—your authentication logic becomes a complex routing mechanism, and your IAM configuration balloons.

The third limitation is lack of flexible role mapping. With raw web identity federation, the connection between an external identity and an AWS role is relatively fixed. If you want different users from the same provider to have different levels of AWS access, you’re limited in how elegantly you can express that. The condition keys available in IAM policies for web identity federation are somewhat constrained compared to what you get with a dedicated identity service.

Finally, raw web identity federation makes it difficult to support anonymous users. If you want to allow users to interact with your application before they authenticate—perhaps browsing a catalog stored in S3—you’d need a separate mechanism entirely. There’s no built-in concept of unauthenticated access in raw web identity federation.

Introducing Amazon Cognito Identity Pools#

Amazon Cognito Identity Pools (also called Cognito Identities, distinct from Cognito User Pools which handle authentication separately) were designed specifically to address these limitations. Cognito Identity Pools act as an abstraction layer between your external identity providers and AWS.

Instead of your application directly exchanging external tokens for AWS credentials, it exchanges them with Cognito Identity Pools first. Cognito then handles the exchange with STS on your behalf. This additional step might seem like unnecessary overhead, but it actually provides tremendous value through the features it enables.

The flow works like this: Your user logs in with Google, Facebook, or another provider. Your app receives an ID token and sends it to Cognito Identity Pools along with information about which provider authenticated the user. Cognito validates the token with the provider and returns an identity ID to your application. Your app can then use this identity ID to request temporary AWS credentials from Cognito, which handles the STS AssumeRoleWithWebIdentity call internally. Finally, your app uses those credentials to access AWS services.

Setting up Cognito Identity Pools requires creating an identity pool and configuring it to trust your external identity providers. Here’s a simplified example using the AWS CLI:

aws cognito-identity create-identity-pool \
  --identity-pool-name "MyMobileAppPool" \
  --allow-unauthenticated-identities \
  --supported-login-providers '{"accounts.google.com":"YOUR_GOOGLE_CLIENT_ID","graph.facebook.com":"YOUR_FACEBOOK_APP_ID"}'

Once your identity pool is created, you’d configure IAM roles for both authenticated and unauthenticated access. Cognito automatically maps users to these roles based on their authentication status and can apply sophisticated role-mapping rules.

From your application’s perspective, using Cognito is similarly straightforward:

import { CognitoIdentityClient } from "@aws-sdk/client-cognito-identity";
import { fromCognitoIdentityPool } from "@aws-sdk/credential-providers";

const cognitoIdentityClient = new CognitoIdentityClient({ region: "us-east-1" });

async function getAwsCredentialsWithCognito(googleIdToken) {
  const identityId = await cognitoIdentityClient.getId({
    IdentityPoolId: "us-east-1:12345678-1234-1234-1234-123456789012",
    Logins: {
      "accounts.google.com": googleIdToken
    }
  });

  // Cognito automatically handles credential retrieval
  const credentials = await fromCognitoIdentityPool({
    client: cognitoIdentityClient,
    identityPoolId: "us-east-1:12345678-1234-1234-1234-123456789012",
    logins: {
      "accounts.google.com": googleIdToken
    }
  })();

  return credentials;
}

How Cognito Identity Pools Solves the Problems#

Now let’s examine how Cognito Identity Pools elegantly addresses each limitation we identified.

Token refresh and lifecycle management: Cognito handles token refresh transparently. When you request credentials through Cognito using fromCognitoIdentityPool, the credential provider automatically manages refresh logic. If your Google token expires, Cognito can request a new one (assuming you’ve provided a refresh token), and your credential provider will seamlessly update your AWS credentials. Your application doesn’t need to explicitly orchestrate multiple token refresh cycles.

Unifying multiple identity providers: With Cognito Identity Pools, you configure all your identity providers in a single place. Users can authenticate with any supported provider, and Cognito treats them consistently. Behind the scenes, Cognito maps all these different identities to a single conceptual user (using an identity ID), regardless of which provider they used. If the same person logs in with Google one day and Facebook the next, Cognito can recognize it’s the same user and maintain continuity. This unification is optional but powerful when you need it.

Flexible role mapping: Cognito Identity Pools introduces Enhanced Flow with role mapping rules. Instead of having a single fixed role per provider, you can define rules that dynamically map users to different roles based on claims in their token. For example, you could assign premium users to a role with S3 access and free users to a more restricted role, all based on information in the identity provider’s token.

Supporting anonymous users: Cognito Identity Pools has built-in support for unauthenticated identities. You can enable this when creating your identity pool, and users who haven’t logged in yet still receive an identity ID and can be assigned to an unauthenticated role. This means your app can support anonymous browsing or limited functionality before requiring login, without needing separate infrastructure.

When Raw Web Identity Federation Still Makes Sense#

It would be misleading to say that raw web identity federation has no place in modern AWS applications. There are specific scenarios where the directness of raw web identity federation is genuinely appropriate.

If you’re building a simple, single-provider application where you only need to support one identity provider, have straightforward token management, and don’t need role mapping or anonymous access, raw web identity federation keeps things lean. The fewer moving parts, the fewer things that can fail.

In scenarios with very strict infrastructure minimalism requirements, some teams prefer to avoid running Cognito for policy or compliance reasons. Raw web identity federation gives you federation without introducing another managed service into your architecture.

Additionally, if you’re building internal tools or proof-of-concepts where sophisticated user management isn’t required, the added complexity of Cognito might genuinely be unnecessary.

However, these scenarios represent a minority of real-world applications. For most mobile and web applications serving external users, the trade-offs favor Cognito.

Practical Considerations: Security and Best Practices#

Regardless of which approach you choose, certain security principles apply to both.

Token validation is critical. Whether you’re using raw web identity federation or Cognito, never trust a token without verifying it with the issuing provider. AWS performs this verification for you in both cases, but ensure your application doesn’t create alternate code paths that skip this validation.

HTTPS enforcement is non-negotiable. Token exchange should only happen over encrypted connections. This isn’t optional—it’s fundamental to protecting user credentials and session tokens.

Short-lived credentials are a core principle of both approaches. The temporary credentials issued by AWS STS are intentionally short-lived (typically one hour or less). Never store them permanently or try to circumvent this expiration. If you need persistent access, that’s a sign your architecture needs rethinking.

Regional considerations matter more than they might initially appear. Identity pool IDs are region-specific, and your credential requests should target the same region. Distributing identity pools across regions for redundancy requires careful planning.

One often-overlooked best practice: validate that the identity ID hasn’t changed between requests when using Cognito. If a user logs out and a new user logs in on the same device, you need a fresh identity ID. The Cognito SDK handles this, but if you’re implementing custom logic, it’s easy to miss.

A Practical Decision Framework#

When evaluating these two approaches for a new project, ask yourself these questions in order:

First, how many identity providers do you need to support? If it’s just one and you’re confident that won’t change, raw web identity federation becomes more defensible. If you anticipate supporting multiple providers now or in the future, Cognito is the stronger choice.

Second, do you need anonymous or unauthenticated access? If yes, Cognito is essentially required. If no, both approaches work.

Third, do different users need different levels of AWS access based on attributes in their identity? Role mapping rules in Cognito are elegant for this. If all users get identical permissions, raw web identity federation is simpler.

Fourth, how sophisticated is your token refresh requirement? If you need robust, transparent token refresh and credential rotation, Cognito’s credential provider handles this beautifully. If you want explicit control over refresh timing, raw web identity federation gives you that control (at the cost of complexity).

Finally, what’s your team’s operational burden capacity? Cognito is another service to understand and monitor, but it’s also another service you don’t have to implement yourself. Raw web identity federation requires you to own more of the token management logic in your application.

Let’s ground this in a concrete scenario. Imagine you’re building a photo-sharing mobile app where users log in with Google or Facebook, upload photos to S3, and can share them with others.

With raw web identity federation, you’d create two IAM roles—one for Google-authenticated users and one for Facebook users. Both roles would have S3 permissions. Your mobile app would need to detect which provider a user chose, get the appropriate token, exchange it for credentials, and handle token refresh on its own. If you later want to support anonymous browsing of public photos, you’d need to build that separately. Managing which user uploaded which photo becomes tricky because your AWS credentials don’t inherently carry identity information beyond which provider they came from.

With Cognito Identity Pools, you’d create a single identity pool supporting both Google and Facebook. You’d enable unauthenticated identities and create two IAM roles: one for authenticated users (full S3 permissions) and one for anonymous users (read-only S3 permissions). Cognito automatically handles token refresh, maps all users consistently, and your credential provider transparently manages refresh. When you write data to DynamoDB with metadata about the photo, you can retrieve the identity ID from Cognito’s context, giving you a clean way to track ownership. Adding Apple Sign-In later is just adding another provider to your identity pool—no role changes required.

The Cognito approach gives you cleaner code, more flexible access control, and better scalability as your app grows.

The Future: Cognito User Pools vs Identity Pools#

A quick clarification for those just learning AWS authentication: Amazon Cognito actually comprises two distinct services. Cognito User Pools handle authentication and user management (sign-up, sign-in, password reset, etc.). Cognito Identity Pools handle authorization and federation with external providers. A complete solution often uses both—Cognito User Pools for your own user directory, and Cognito Identity Pools to federate with external providers and issue AWS credentials.

This distinction sometimes confuses developers, but it’s useful: User Pools are about authentication (proving who you are), while Identity Pools are about authorization and federation (granting AWS access). For the purpose of this article, we’ve focused on Identity Pools, but knowing this distinction will make your AWS journey clearer.

Conclusion#

The choice between raw web identity federation and Cognito Identity Pools isn’t about which is “better” in absolute terms—it’s about which fits your specific requirements. Raw web identity federation is simpler in concept and has minimal overhead if your needs are truly minimal. However, for most real-world applications that need to scale, support multiple providers, or handle complex authorization scenarios, Cognito Identity Pools provides a more elegant, maintainable solution.

The key insight is this: Cognito Identity Pools aren’t just a convenience—they’re a purpose-built solution to a set of problems that arise naturally as applications grow. Token refresh, identity unification across providers, flexible role mapping, and anonymous access support aren’t features you’ll need immediately, but they’re features you’ll be grateful to have as your user base grows.

As you build your next mobile or web application requiring AWS federation, consider starting with Cognito Identity Pools unless you have a specific reason not to. Your future self—and your operations team—will appreciate the reduced complexity and increased flexibility that this abstraction layer provides.