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Chapter 25 of 118
Adds user authentication to web and mobile apps with Amazon Cognito (user pools and identity pools) and the AWS Amplify client auth libraries.
6 minutes · 1,353 words · 9 sections
Application-level user authentication and authorization with Amazon Cognito and the Amplify client auth libraries. Verify specific limits, quotas, and exact API shapes against official AWS documentation when precision matters; trust the docs over memory when they conflict.
Recommended: The AWS MCP server provides streamlined access to the AWS APIs used in this skill (Cognito user pool/app client/identity pool setup, API Gateway authorizers). If it is unavailable, the AWS CLI commands shown throughout work directly — the skill has no hard dependency on MCP.
When NOT to use: Amplify Gen2 backend code (defineAuth, amplify/auth.ts, npx ampx); IAM
policy/role/trust-policy authoring, STS, or IAM Identity Center console SSO; API Gateway
route/integration setup or Lambda function implementation (this skill covers only the Cognito/JWT
authorizer configuration and the purpose of Cognito Lambda triggers).
These are different services that are frequently confused. Most apps need a user pool; add an identity pool only if the client must call AWS services directly.
| You need… | Use | Why |
|---|---|---|
| Sign-up / sign-in, user directory, issue JWTs | User pool | It authenticates users and is an OIDC IdP |
| The signed-in client to call S3/DynamoDB/etc. directly with AWS credentials | Identity pool | It exchanges a token for temporary AWS credentials via STS |
| Both (sign in, then hit AWS resources from the browser/app) | User pool → identity pool | Identity pool trusts the user pool as its IdP |
If your app only calls your own backend/API, you do not need an identity pool — send the user pool token to your API. See identity-pools.md (opens in a new tab).
update-user-pool-client and set-identity-pool-roles are FULL REPLACE, not partial updates: Any field you omit is reset to its default — calling update-user-pool-client with only the fields you want to change silently wipes ExplicitAuthFlows, token validity, EnableTokenRevocation, refresh-token rotation, and read/write attributes; set-identity-pool-roles likewise replaces the whole roles + RoleMappings structure. Always read-modify-write: describe-user-pool-client (or get-identity-pool-roles) first, then re-send every existing field plus your change. In an agent context the wipe is invisible — the call succeeds and only breaks later when a user hits the missing flow. See managed-login-oauth.md (opens in a new tab) and identity-pools.md (opens in a new tab).
Don’t use the implicit grant for new apps: The implicit grant (response_type=token) is legacy and returns tokens in the URL fragment. Use the authorization code grant with PKCE (response_type=code + code_challenge) for SPAs and mobile — public clients, no client secret. See managed-login-oauth.md (opens in a new tab).
Don’t store refresh tokens in localStorage for high-value apps: localStorage is readable by any injected script (XSS). The Amplify client library defaults to localStorage; switch to cookieStorage, keep refresh-token lifetime short, and enable refresh token rotation + token revocation on the app client. See tokens-and-sessions.md (opens in a new tab).
Access-token claim customization needs a paid feature plan: The pre token generation trigger customizes the ID token on the entry-level plan (V1), but customizing the access token (V2/V3) requires a paid feature plan — check the Cognito feature plans documentation (opens in a new tab) for which plan currently includes this, as plan names and inclusions can change. Don’t assume access-token claims work on the entry-level plan. See lambda-triggers.md (opens in a new tab).
App client secret + SPA = broken auth: A public client (browser/mobile) must have no client secret. If a secret is set, token calls fail unless a SECRET_HASH is sent, which a browser cannot protect. Generate a secret only for confidential (server-side) clients.
Don’t bulk admin-confirm-sign-up UNCONFIRMED users: When users are stuck UNCONFIRMED, prefer resend-confirmation-code so each user re-verifies via confirm-sign-up and proves email ownership (the code likely expired or went to spam). admin-confirm-sign-up flips the status instantly but confirms the account without verifying the email — the attribute stays unverified, which is dangerous when email drives password reset or account linking. Reserve it for trusted/migrated accounts. See troubleshooting.md (opens in a new tab).
| You want to… | Go to |
|---|---|
| Create a user pool, sign-up/sign-in, MFA, password policy, app clients | user-pools.md (opens in a new tab) |
| Add hosted UI / managed login, OAuth flows, social or SAML login, callback URLs, custom domain (ACM in us-east-1) | managed-login-oauth.md (opens in a new tab) |
| Handle ID/access/refresh tokens, rotation, revocation, session termination (global sign-out vs revoke vs disable) | tokens-and-sessions.md (opens in a new tab) |
| Give the client temporary AWS credentials, guest access, role mapping | identity-pools.md (opens in a new tab) |
| Protect an API Gateway API with Cognito tokens (and enforce custom claims in the backend) | api-authorization.md (opens in a new tab) |
Add Cognito login in front of an Application Load Balancer (ALB authenticate-cognito) | api-authorization.md (opens in a new tab) |
| Machine-to-machine (client credentials) auth, resource servers, custom scopes | managed-login-oauth.md (opens in a new tab) |
Create user pool groups and add users to them (cognito:groups, Precedence) | user-pools.md (opens in a new tab) |
| Customize claims, custom auth challenge flows, migrate users, validate sign-up | lambda-triggers.md (opens in a new tab) |
Add passkey / WebAuthn sign-in (USER_AUTH flow, AllowedFirstAuthFactors, WebAuthn enrollment) | passkeys.md (opens in a new tab) |
| Configure threat protection — compromised-credentials block, adaptive auth (risk-based MFA), log delivery to CloudWatch | threat-protection.md (opens in a new tab) |
| Something is broken (redirect, token, MFA, CORS, social login) | troubleshooting.md (opens in a new tab) |
“Add sign-up and login to my React app” → Create a user pool + a public app client (no secret), enable the hosted UI / managed login with the authorization code grant with PKCE, wire the Amplify client library. See user-pools.md (opens in a new tab) and managed-login-oauth.md (opens in a new tab).
“Add Google / social login” → Register the social IdP on the user pool, map attributes, add the provider to the app client and hosted UI. See managed-login-oauth.md (opens in a new tab).
“Only authenticated users should call my API” → HTTP API → JWT authorizer; REST API → Cognito user pools authorizer. See api-authorization.md (opens in a new tab).
“Let the browser upload to S3 after login” → User pool for sign-in, then an identity pool to vend scoped temporary credentials. See identity-pools.md (opens in a new tab).
| Error/Symptom | Likely Cause | Quick Fix |
|---|---|---|
redirect_mismatch / redirect to wrong URL after login | Callback URL not registered, or scheme/trailing-slash/case differs | Add the exact callback URL (incl. scheme and path) to the app client’s Allowed callback URLs |
| Token calls fail with “unable to verify secret hash” | Client secret set on a public (SPA/mobile) client | Recreate the app client with no secret, or send SECRET_HASH from a confidential client |
| Users get 401 from API Gateway with a valid token | Wrong token type or audience/issuer mismatch | HTTP JWT authorizer: issuer https://cognito-idp.{region}.amazonaws.com/{userPoolId}, audience = app client id; send the token the authorizer expects |
| CORS errors calling the hosted UI / token endpoint | Browser calling /oauth2/token cross-origin, or missing CORS on your API | Do the code exchange with PKCE; don’t proxy the token endpoint from the browser |
| Social login user “already exists” / attribute conflict | Same email across providers creates separate users | Enable attribute mapping + account linking; treat email as non-unique across IdPs |
Full tables in troubleshooting.md (opens in a new tab).
cookieStorage over localStorage.iss, aud/client_id, token_use, exp) on every protected request. Use a maintained library such as aws-jwt-verify (opens in a new tab) rather than hand-rolling verification.Content-Security-Policy (restrict script sources to mitigate token-stealing XSS), Strict-Transport-Security (HSTS), X-Frame-Options/frame-ancestors (clickjacking on login pages), and X-Content-Type-Options: nosniff.When you need depth beyond this skill — exact parameter shapes, current limits, edge behaviors — fall back to the authoritative AWS sources rather than guessing. Pointers age much slower than content, so this map stays useful without the skill having to grow.
defineAuth, amplify/auth.ts, npx ampx sandbox).Install this repository
npx skills add aws/agent-toolkit-for-aws/plugin marketplace add aws/agent-toolkit-for-awsSkills install per repository, not per chapter — the CLI has no documented per-skill form, so we do not print one.
Adds user authentication to web and mobile apps with Amazon Cognito (user pools and identity pools) and the AWS Amplify client auth libraries. Covers sign-up/sign-in flows and the login page (Cognito-hosted UI / managed login), MFA, password policies, OAuth 2.0 / OIDC flows (auth-code + PKCE, client credentials), social/SAML federation, tokens (ID/access/refresh, rotation, revocation, storage), Cognito Lambda triggers, identity pools (temp AWS creds), and gating API Gateway (or ALB) routes to signed-in users via Cognito/JWT authorizers. Applies when adding a login or sign-up page, configuring a user pool or app client, choosing user pool vs identity pool, wiring social/SAML, refreshing tokens, requiring sign-in on an API Gateway or ALB, or debugging redirect_uri/token/MFA/CORS/federation errors. Does NOT cover Amplify Gen2 backend definitions (defineAuth, npx ampx → aws-amplify), IAM/STS/Identity Center (→ aws-iam), or API Gateway/Lambda resource config beyond the authorizer (→ aws-serverless).
The verbatim description from this skill’s front matter — the string an agent matches on to decide whether to load it.
main, last pushed 10 August 2026.SKILL.md, not by matching a directory convention. 16 distinct layouts observed: plugins/aws-agents-for-devsecops/skills/*/SKILL.md, plugins/aws-agents/skills/*/SKILL.md, plugins/aws-core/skills/*/SKILL.md, skills/core-skills/*/SKILL.md, skills/specialized-skills/analytics-skills/*/SKILL.md, skills/specialized-skills/database-skills/*/SKILL.md, skills/specialized-skills/ec2-skills/*/SKILL.md, skills/specialized-skills/migration-and-modernization-skills/*/SKILL.md, skills/specialized-skills/networking-and-content-delivery-skills/*/SKILL.md, skills/specialized-skills/operations-skills/*/SKILL.md, skills/specialized-skills/resilience-skills/*/SKILL.md, skills/specialized-skills/security-and-identity-skills/*/SKILL.md, skills/specialized-skills/serverless-skills/*/SKILL.md, skills/specialized-skills/storage-skills/*/SKILL.md, skills/specialized-skills/system-table-skills/*/SKILL.md, skills/specialized-skills/web-and-mobile-development/*/SKILL.md.h1 and no skipped levels:.claude-plugin/marketplace.json by Amazon Web Services, declaring 4 plugins. It is read for editorial metadata only — never as the skill index, which is always the repository tree./aws/agent-toolkit-for-aws.md, and each chapter at its own .md URL.9 files · 71 KB
Everything this skill ships beside its prose. All of it is set here, as subchapters of chapter 25.
Documentation the agent loads on demand, rather than up front.