AWS Auth (Amazon Cognito)

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).

User Pool vs Identity Pool — pick first

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.

Critical Warnings

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 and identity-pools.md.

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.

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.

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 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.

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.

Quick Navigation

You want to...	Go to
Create a user pool, sign-up/sign-in, MFA, password policy, app clients	user-pools.md
Add hosted UI / managed login, OAuth flows, social or SAML login, callback URLs, custom domain (ACM in us-east-1)	managed-login-oauth.md
Handle ID/access/refresh tokens, rotation, revocation, session termination (global sign-out vs revoke vs disable)	tokens-and-sessions.md
Give the client temporary AWS credentials, guest access, role mapping	identity-pools.md
Protect an API Gateway API with Cognito tokens (and enforce custom claims in the backend)	api-authorization.md
Add Cognito login in front of an Application Load Balancer (ALB authenticate-cognito)	api-authorization.md
Machine-to-machine (client credentials) auth, resource servers, custom scopes	managed-login-oauth.md
Create user pool groups and add users to them (cognito:groups, Precedence)	user-pools.md
Customize claims, custom auth challenge flows, migrate users, validate sign-up	lambda-triggers.md
Add passkey / WebAuthn sign-in (USER_AUTH flow, AllowedFirstAuthFactors, WebAuthn enrollment)	passkeys.md
Configure threat protection — compromised-credentials block, adaptive auth (risk-based MFA), log delivery to CloudWatch	threat-protection.md
Something is broken (redirect, token, MFA, CORS, social login)	troubleshooting.md

Common Workflows

"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 and managed-login-oauth.md.

"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.

"Only authenticated users should call my API" → HTTP API → JWT authorizer; REST API → Cognito user pools authorizer. See api-authorization.md.

"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.

Troubleshooting

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.

Security Considerations

• Public clients (SPA/mobile): no client secret, authorization code grant with PKCE, request least-privilege scopes.
• Enable MFA (TOTP or SMS), a strong password policy, and advanced security / threat protection where available.
• Short access-token lifetime; enable refresh token rotation and token revocation; prefer cookieStorage over localStorage.
• Identity pools: scope the authenticated IAM role tightly; disable unauthenticated (guest) access unless required.
• Validate JWTs against the user pool JWKS (iss, aud/client_id, token_use, exp) on every protected request. Use a maintained library such as aws-jwt-verify rather than hand-rolling verification.
• Set security headers on the app's web pages: 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.
• Enable logging and monitoring: CloudTrail for Cognito API events (sign-up/sign-in/admin), user pool threat protection (adaptive auth + event logging), CloudWatch alarms on failed/throttled auth, and API Gateway access logging for authorizer decisions.
• All Cognito and API endpoints are HTTPS/TLS only; enable encryption at rest with a customer-managed KMS key (and restricted key access) on CloudWatch Log groups, SNS topics used for MFA/notifications, and any identity-pool-fronted upload buckets.
• If using SNS for MFA/notification delivery, enable server-side encryption (KMS) on the topic, and keep SMS/email message content limited to what the recipient needs — don't include more PII than the message requires.
• References: Amazon Cognito security features (user pools), Amazon Cognito security (top-level, incl. identity pools), and IAM/STS best practices.

Where to Look When This Skill Is Silent

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.

• API reference (exact params, defaults, errors): Cognito User Pools API and Cognito Identity API
• Developer Guide (concepts, workflows): Amazon Cognito Developer Guide
• Quotas, rate limits, session-cookie lifetime: Cognito quotas
• Feature plans / tier gating: Cognito feature plans
• Pricing: Amazon Cognito pricing
• CLI reference: aws cognito-idp and aws cognito-identity

Not Covered By This Skill

• Amplify Gen2 backend (defineAuth, amplify/auth.ts, npx ampx sandbox).
• IAM policy/role/trust-policy authoring, STS, IAM Identity Center console SSO.
• API Gateway route/integration setup and Lambda function implementation (this skill covers only the Cognito/JWT authorizer configuration and the purpose of Cognito Lambda triggers).