AWS Cognito

Amazon Cognito provides authentication, authorization, and user management for web and mobile applications. Users can sign in directly or through federated identity providers.

Table of Contents

• Core Concepts
• Common Patterns
• CLI Reference
• Best Practices
• Troubleshooting
• References

Core Concepts

User Pools

User directory for sign-up and sign-in. Provides:

• User registration and authentication
• OAuth 2.0 / OpenID Connect tokens
• MFA and password policies
• Customizable UI and flows

Identity Pools (Federated Identities)

Provide temporary AWS credentials to access AWS services. Users can be:

• Cognito User Pool users
• Social identity (Google, Facebook, Apple)
• SAML/OIDC enterprise identity
• Anonymous guests

Tokens

Common Patterns

Create User Pool

AWS CLI:

aws cognito-idp create-user-pool \
  --pool-name my-app-users \
  --policies '{
    "PasswordPolicy": {
      "MinimumLength": 12,
      "RequireUppercase": true,
      "RequireLowercase": true,
      "RequireNumbers": true,
      "RequireSymbols": true
    }
  }' \
  --auto-verified-attributes email \
  --username-attributes email \
  --mfa-configuration OPTIONAL \
  --user-attribute-update-settings '{
    "AttributesRequireVerificationBeforeUpdate": ["email"]
  }'

Create App Client

aws cognito-idp create-user-pool-client \
  --user-pool-id us-east-1_abc123 \
  --client-name my-web-app \
  --generate-secret \
  --explicit-auth-flows ALLOW_USER_SRP_AUTH ALLOW_REFRESH_TOKEN_AUTH \
  --supported-identity-providers COGNITO \
  --callback-urls https://myapp.com/callback \
  --logout-urls https://myapp.com/logout \
  --allowed-o-auth-flows code \
  --allowed-o-auth-scopes openid email profile \
  --allowed-o-auth-flows-user-pool-client \
  --access-token-validity 60 \
  --id-token-validity 60 \
  --refresh-token-validity 30 \
  --token-validity-units '{
    "AccessToken": "minutes",
    "IdToken": "minutes",
    "RefreshToken": "days"
  }'

Sign Up User

import boto3
import hmac
import hashlib
import base64

cognito = boto3.client('cognito-idp')

def get_secret_hash(username, client_id, client_secret):
    message = username + client_id
    dig = hmac.new(
        client_secret.encode('utf-8'),
        message.encode('utf-8'),
        digestmod=hashlib.sha256
    ).digest()
    return base64.b64encode(dig).decode()

response = cognito.sign_up(
    ClientId='client-id',
    SecretHash=get_secret_hash('user@example.com', 'client-id', 'client-secret'),
    Username='user@example.com',
    Password='SecurePassword123!',
    UserAttributes=[
        {'Name': 'email', 'Value': 'user@example.com'},
        {'Name': 'name', 'Value': 'John Doe'}
    ]
)

Confirm Sign Up

cognito.confirm_sign_up(
    ClientId='client-id',
    SecretHash=get_secret_hash('user@example.com', 'client-id', 'client-secret'),
    Username='user@example.com',
    ConfirmationCode='123456'
)

Authenticate User

response = cognito.initiate_auth(
    ClientId='client-id',
    AuthFlow='USER_SRP_AUTH',
    AuthParameters={
        'USERNAME': 'user@example.com',
        'SECRET_HASH': get_secret_hash('user@example.com', 'client-id', 'client-secret'),
        'SRP_A': srp_a  # From SRP library
    }
)

# For simple password auth (not recommended for production)
response = cognito.admin_initiate_auth(
    UserPoolId='us-east-1_abc123',
    ClientId='client-id',
    AuthFlow='ADMIN_USER_PASSWORD_AUTH',
    AuthParameters={
        'USERNAME': 'user@example.com',
        'PASSWORD': 'password',
        'SECRET_HASH': get_secret_hash('user@example.com', 'client-id', 'client-secret')
    }
)

tokens = response['AuthenticationResult']
id_token = tokens['IdToken']
access_token = tokens['AccessToken']
refresh_token = tokens['RefreshToken']

Refresh Tokens

response = cognito.initiate_auth(
    ClientId='client-id',
    AuthFlow='REFRESH_TOKEN_AUTH',
    AuthParameters={
        'REFRESH_TOKEN': refresh_token,
        'SECRET_HASH': get_secret_hash('user@example.com', 'client-id', 'client-secret')
    }
)

Create Identity Pool

aws cognito-identity create-identity-pool \
  --identity-pool-name my-app-identities \
  --allow-unauthenticated-identities \
  --cognito-identity-providers \
    ProviderName=cognito-idp.us-east-1.amazonaws.com/us-east-1_abc123,\
ClientId=client-id,\
ServerSideTokenCheck=true

Get AWS Credentials

import boto3

cognito_identity = boto3.client('cognito-identity')

# Get identity ID
response = cognito_identity.get_id(
    IdentityPoolId='us-east-1:12345678-1234-1234-1234-123456789012',
    Logins={
        'cognito-idp.us-east-1.amazonaws.com/us-east-1_abc123': id_token
    }
)
identity_id = response['IdentityId']

# Get credentials
response = cognito_identity.get_credentials_for_identity(
    IdentityId=identity_id,
    Logins={
        'cognito-idp.us-east-1.amazonaws.com/us-east-1_abc123': id_token
    }
)

credentials = response['Credentials']
# Use credentials['AccessKeyId'], credentials['SecretKey'], credentials['SessionToken']

CLI Reference

User Pool

Users

Authentication

Best Practices

Security

• Enable MFA for all users (at least optional)
• Use strong password policies
• Enable advanced security features (adaptive auth)
• Verify email/phone before allowing sign-in
• Use short token lifetimes for sensitive apps
• Never expose client secrets in frontend code

User Experience

• Use hosted UI for quick implementation
• Customize UI with CSS
• Implement proper error handling
• Provide clear password requirements

Architecture

• Use identity pools for AWS resource access
• Use access tokens for API Gateway
• Store refresh tokens securely
• Implement token refresh before expiry

Troubleshooting

User Cannot Sign In

Causes:

• User not confirmed
• Password incorrect
• User disabled
• Account locked (too many attempts)

Debug:

aws cognito-idp admin-get-user \
  --user-pool-id us-east-1_abc123 \
  --username user@example.com

Token Validation Failed

Causes:

• Token expired
• Wrong user pool/client ID
• Token signature invalid

Validate JWT:

import jwt
import requests

# Get JWKS
jwks_url = f'https://cognito-idp.us-east-1.amazonaws.com/us-east-1_abc123/.well-known/jwks.json'
jwks = requests.get(jwks_url).json()

# Decode and verify (use python-jose or similar)
from jose import jwt

claims = jwt.decode(
    token,
    jwks,
    algorithms=['RS256'],
    audience='client-id',
    issuer='https://cognito-idp.us-east-1.amazonaws.com/us-east-1_abc123'
)

Hosted UI Not Working

Check:

• Callback URLs configured correctly
• Domain configured for user pool
• OAuth settings enabled

# Check domain
aws cognito-idp describe-user-pool \
  --user-pool-id us-east-1_abc123 \
  --query 'UserPool.Domain'

Rate Limiting

Symptom: TooManyRequestsException

Solutions:

• Implement exponential backoff
• Request quota increase
• Cache tokens appropriately

References

• Cognito Developer Guide
• Cognito User Pools API
• Cognito Identity API
• Cognito CLI Reference