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.

[Core Concepts](#core-concepts)
[Common Patterns](#common-patterns)
[CLI Reference](#cli-reference)
[Best Practices](#best-practices)
[Troubleshooting](#troubleshooting)
[References](#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

| Token | Purpose | Lifetime | |-------|---------|----------| | ID Token | User identity claims | 1 hour | | Access Token | API authorization | 1 hour | | Refresh Token | Get new ID/Access tokens | 30 days (configurable) |

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

| Command | Description | |---------|-------------| | aws cognito-idp create-user-pool | Create user pool | | aws cognito-idp describe-user-pool | Get pool details | | aws cognito-idp update-user-pool | Update pool settings | | aws cognito-idp delete-user-pool | Delete pool | | aws cognito-idp list-user-pools | List pools |

Users

| Command | Description | |---------|-------------| | aws cognito-idp admin-create-user | Create user (admin) | | aws cognito-idp admin-delete-user | Delete user | | aws cognito-idp admin-get-user | Get user details | | aws cognito-idp list-users | List users | | aws cognito-idp admin-set-user-password | Set password | | aws cognito-idp admin-disable-user | Disable user |

Authentication

| Command | Description | |---------|-------------| | aws cognito-idp initiate-auth | Start authentication | | aws cognito-idp respond-to-auth-challenge | Respond to MFA | | aws cognito-idp admin-initiate-auth | Admin 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