IAM roles - Amazon Cognito

IAM roles

While creating an identity pool, you're prompted to update the IAM roles that your users assume. IAM roles work like this: When a user logs in to your app, Amazon Cognito generates temporary AWS credentials for the user. These temporary credentials are associated with a specific IAM role. With the IAM role, you can define a set of permissions to access your AWS resources.

You can specify default IAM roles for authenticated and unauthenticated users. In addition, you can define rules to choose the role for each user based on claims in the user's ID token. For more information, see Using role-based access control.

By default, the Amazon Cognito console creates IAM roles that provide access to Amazon Mobile Analytics and to Amazon Cognito Sync. Alternatively, you can choose to use existing IAM roles.

Modify IAM roles to allow or restrict access to other services. To do so, log in to the IAM Console. Then select Roles, and select a role. The policies attached to the selected role are listed in the Permissions tab. You can customize an access policy by selecting the corresponding Manage Policy link. To learn more about using and defining policies, see Overview of IAM Policies.


As a best practice, define policies that follow the principle of granting least privilege. In other words, the policies include only the permissions that users require to perform their tasks. For more information, see Grant Least Privilege in the IAM User Guide.

Remember that unauthenticated identities are assumed by users who do not log in to your app. Typically, the permissions that you assign for unauthenticated identities should be more restrictive than those for authenticated identities.

Set up a trust policy

Amazon Cognito uses IAM roles to generate temporary credentials for your application's users. Access to permissions is controlled by a role's trust relationships. Learn more about Role trust and permissions.

The token presented to AWS STS is generated by an identity pool, which translates a user pool, social, or OIDC provider token, or a SAML assertion, to its own token. The identity pool token contains an aud claim that is the identity pool ID.

The following example role trust policy allows the federated service principal cognito-identity.amazonaws.com to call the AWS STS API AssumeRoleWithWebIdentity. The request will only succeed if the identity pool token in the API request has the following claims.

  1. An aud claim of the identity pool ID us-west-2:abcdefg-1234-5678-910a-0e8443553f95.

  2. An amr claim of authenticated that is added when the user has signed in and isn't a guest user.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Principal": { "Federated": "cognito-identity.amazonaws.com" }, "Action": "sts:AssumeRoleWithWebIdentity", "Condition": { "StringEquals": { "cognito-identity.amazonaws.com:aud": "us-west-2:abcdefg-1234-5678-910a-0e8443553f95" }, "ForAnyValue:StringLike": { "cognito-identity.amazonaws.com:amr": "authenticated" } } } ] }

Trust policies for IAM roles in Basic (Classic) authentication

You must apply at least one condition that limits trust policies for roles that you use with identity pools. When you create or update role trust policies for identity pools, IAM returns an error if you try to save your changes without at least one condition key that limits source identities. AWS STS doesn't permit cross-account AssumeRoleWithWebIdentity operations from identity pools to IAM roles that lack a condition of this type.

This topic includes several conditions that limit source identities for identity pools. For a full list, see Available keys for AWS web identity federation.

In basic, or classic, authentication with an identity pool, you can assume any IAM role with AWS STS if it has the right trust policy. IAM roles for Amazon Cognito identity pools trust the service principal cognito-identity.amazonaws.com to assume the role. This configuration is not sufficient to secure your IAM roles against unintended access to resources. Roles of this type must apply an additional condition to the role trust policy. You can't create or modify roles for identity pools without at least one of the following conditions.


Restricts the role to operations from one or more identity pools. Amazon Cognito indicates the source identity pool in the aud claim in the identity pool token.


Restricts the role to either authenticated or unauthenticated (guest) users. Amazon Cognito indicates the authentication state in the amr claim in the identity pool token.


Restricts the role to one or more users by UUID. This UUID is the user's identity ID in the identity pool. This value isn’t the sub value from the user’s original identity provider. Amazon Cognito indicates this UUID in the sub claim in the identity pool token.

Enhanced-flow authentication requires that the IAM role be in the same AWS account as the identity pool, but this isn't the case in basic authentication.

Additional considerations apply to Amazon Cognito identity pools that assume cross-account IAM roles. The trust policies of those roles must accept the cognito-identity.amazonaws.com service principal and must contain the specific cognito-identity.amazonaws.com:aud condition. To prevent unintended access to your AWS resources, the aud condition key restricts the role to users from the identity pools in the condition value.

The token that an identity pool issues for an identity contains information about the originating AWS account of the identity pool. When you present an identity pool token in an AssumeRoleWithWebIdentity API request, AWS STS checks to see if the originating identity pool is in the same AWS account as the IAM role. If AWS STS determines that the request is cross-account, it checks to see if the role trust policy has an aud condition. The assume-role call fails if no such conditions are present in the role trust policy. If the request is not cross-account, AWS STS doesn’t enforce this restriction. As a best practice, always apply a condition of this type to the trust policies of your identity pool roles.

Additional trust policy conditions

Reuse roles across identity pools

To reuse a role across multiple identity pools, because they share a common permission set, you can include multiple identity pools, like this:

"StringEquals": { "cognito-identity.amazonaws.com:aud": [ "us-east-1:12345678-abcd-abcd-abcd-123456790ab", "us-east-1:98765432-dcba-dcba-dcba-123456790ab" ] }
Limit access to specific identities

To create a policy limited to a specific set of app users, check the value of cognito-identity.amazonaws.com:sub:

"StringEquals": { "cognito-identity.amazonaws.com:aud": "us-east-1:12345678-abcd-abcd-abcd-123456790ab", "cognito-identity.amazonaws.com:sub": [ "us-east-1:12345678-1234-1234-1234-123456790ab", "us-east-1:98765432-1234-1234-1243-123456790ab" ] }
Limit access to specific providers

To create a policy limited to users who have logged in with a specific provider (perhaps your own login provider), check the value of cognito-identity.amazonaws.com:amr:

"ForAnyValue:StringLike": { "cognito-identity.amazonaws.com:amr": "login.myprovider.myapp" }

For example, an app that trusts only Facebook would have the following amr clause:

"ForAnyValue:StringLike": { "cognito-identity.amazonaws.com:amr": "graph.facebook.com" }

Access policies

The permissions that you attach to a role apply to all users who assume that role. To partition your users' access, use policy conditions and variables. For more information, see IAM policy elements: Variables and tags. You can use the sub condition to restrict actions to Amazon Cognito identity IDs in your access policies. Use this option with caution, particularly for unauthenticated identities, which lack a consistent user ID. For more information about the IAM policy variables for web federation with Amazon Cognito, see IAM and AWS STS condition context keys in the AWS Identity and Access Management User Guide.

For additional security protection, Amazon Cognito applies a scope-down policy to credentials that you assign your unauthenticated users in the enhanced flow, using GetCredentialsForIdentity. The scope-down policy adds an Inline session policy and an AWS managed session policy to the IAM policies that you apply to your unauthenticated role. Because you must grant access in both the IAM policies for your role and the session policies, the scope-down policy limits users' access to services other than those in the list that follows.


In the basic (classic) flow, you make your own AssumeRoleWithWebIdentity API request, and can apply these restrictions to the request. As a best security practice, don't assign any permissions above this scope-down policy to unauthenticated users.

Amazon Cognito also prevents authenticated and unauthenticated users from making API requests to Amazon Cognito identity pools and Amazon Cognito Sync. Other AWS services might place restrictions on service access from web identities.

In a successful request with the enhanced flow, Amazon Cognito makes an AssumeRoleWithWebIdentity API request in the background. Among the parameters in this request, Amazon Cognito includes the following.

  1. Your user's identity ID.

  2. The ARN of the IAM role that your user wants to assume.

  3. A policy parameter that adds an inline session policy.

  4. A PolicyArns.member.N parameter whose value is an AWS managed policy that grants additional permissions in Amazon CloudWatch.

Services that unauthenticated users can access

When you use the enhanced flow, the scope-down policies that Amazon Cognito applies to your user's session prevent them from using any services other than those listed in the following table. For a subset of services, only specific actions are allowed.

Category Service


Amazon Data Firehose

Amazon Managed Service for Apache Flink

Application Integration

Amazon Simple Queue Service


Amazon Sumerian¹

Business Applications

Amazon Mobile Analytics

Amazon Simple Email Service


AWS Lambda

Cryptography & PKI

AWS Key Management Service¹


Amazon DynamoDB

Amazon SimpleDB

Front-end Web & Mobile

AWS AppSync

Amazon Location Service

Amazon Simple Notification Service

Amazon Pinpoint

Game Development

Amazon GameLift

Internet of Things (IoT)


Machine Learning

Amazon CodeWhisperer

Amazon Comprehend

Amazon Lex

Amazon Machine Learning

Amazon Personalize

Amazon Polly

Amazon Rekognition

Amazon SageMaker¹

Amazon Textract¹

Amazon Transcribe

Amazon Translate

Management & Governance

Amazon CloudWatch

Amazon CloudWatch Logs

Networking & Content Delivery

Amazon API Gateway

Security, Identity, & Compliance

Amazon Cognito user pools


Amazon Simple Storage Service

¹ For the AWS services in the following table, the inline policy grants a subset of actions. The table displays the available actions in each.

AWS service Maximum permissions for unauthenticated enhanced flow users
AWS Key Management Service





Amazon SageMaker


Amazon Textract



Amazon Sumerian


To grant access to AWS services beyond this list, activate the basic (classic) authentication flow in your identity pool. If your users see NotAuthorizedException errors from AWS services that are allowed by the policies assigned to the IAM role for unauthenticated users, evaluate whether you can remove that service from your use case. If you can't, switch to the basic flow.

The inline session policy

The inline session policy restricts your user's effective permissions from including access to any AWS services outside those in the following list. You must also grant permissions to these AWS services in the policies that you apply to the user's IAM role. A user's effective permissions for an assumed-role session are the intersection of the policies assigned to their role, and their session policy. For more information, see Session policies in the AWS Identity and Access Management User Guide.

Amazon Cognito adds the following inline policy to sessions for your users in AWS Regions that are enabled by default.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "cloudwatch:*", "logs:*", "dynamodb:*", "kinesis:*", "mobileanalytics:*", "s3:*", "ses:*", "sns:*", "sqs:*", "lambda:*", "machinelearning:*", "execute-api:*", "iot:*", "gamelift:*", "scs:*", "cognito-identity:*", "cognito-idp:*", "lex:*", "polly:*", "comprehend:*", "translate:*", "transcribe:*", "rekognition:*", "mobiletargeting:*", "firehose:*", "appsync:*", "personalize:*", "kms:Encrypt", "kms:Decrypt", "kms:ReEncrypt*", "kms:GenerateDataKey*", "sagemaker:InvokeEndpoint", "cognito-sync:*", "sumerian:View*", "codewhisperer:*", "textract:DetectDocumentText", "textract:AnalyzeDocument", "sdb:*" ], "Resource": [ "*" ] } ] }

For all other Regions, the inline scope-down policy includes everything listed in the default Regions except for the following Action statements.

"cognito-sync:*", "sumerian:View*", "codewhisperer:*", "textract:DetectDocumentText", "textract:AnalyzeDocument", "sdb:*"

The AWS managed session policy

Amazon Cognito also limits the scope of unauthenticated users' permissions with the AWS managed policy AmazonCognitoUnAuthedIdentitiesSessionPolicy to your unauthenticated users in the enhanced flow. You must also grant this permission in the policies that you attach to your unauthenticated IAM role.

The AmazonCognitoUnAuthedIdentitiesSessionPolicy managed policy has the following permissions.

{ "Version": "2012-10-17", "Statement": [{ "Effect": "Allow", "Action": [ "rum:PutRumEvents", "polly:*", "comprehend:*", "translate:*", "transcribe:*", "rekognition:*", "mobiletargeting:*", "firehose:*", "personalize:*", "sagemaker:InvokeEndpoint" ], "Resource": "*" }] }

Access policy examples

In this section, you can find example Amazon Cognito access policies that grant your users the minimum permissions necessary to do specific operation. You can further limit the permissions for a given identity ID by using policy variables where possible. For example, using ${cognito-identity.amazonaws.com:sub}. For more information, see Understanding Amazon Cognito Authentication Part 3: Roles and Policies on the AWS Mobile Blog.


As a security best practice, policies should include only the permissions that users require to perform their tasks. This means that you should try to always scope access to an individual identity for objects whenever possible.

Grant an identity read access to a single object in Amazon S3

The following access policy grants read permissions to an identity to retrieve a single object from a given S3 bucket.

{ "Version": "2012-10-17", "Statement": [ { "Action": [ "s3:GetObject" ], "Effect": "Allow", "Resource": ["arn:aws:s3:::mybucket/assets/my_picture.jpg"] } ] }

Grant an identity both read and write access to identity specific paths in Amazon S3

The following access policy grants read and write permissions to access a specific prefix "folder" in an S3 bucket by mapping the prefix to the ${cognito-identity.amazonaws.com:sub} variable.

With this policy, an identity such as us-east-1:12345678-1234-1234-1234-123456790ab inserted via ${cognito-identity.amazonaws.com:sub} can get, put, and list objects into arn:aws:s3:::mybucket/us-east-1:12345678-1234-1234-1234-123456790ab. However, the identity would not be granted access to other objects in arn:aws:s3:::mybucket.

{ "Version": "2012-10-17", "Statement": [ { "Action": ["s3:ListBucket"], "Effect": "Allow", "Resource": ["arn:aws:s3:::mybucket"], "Condition": {"StringLike": {"s3:prefix": ["${cognito-identity.amazonaws.com:sub}/*"]}} }, { "Action": [ "s3:GetObject", "s3:PutObject" ], "Effect": "Allow", "Resource": ["arn:aws:s3:::mybucket/${cognito-identity.amazonaws.com:sub}/*"] } ] }

Assign identities fine-grained access to Amazon DynamoDB

The following access policy provides fine-grained access control to DynamoDB resources using Amazon Cognito environment variables. These variables grant access to items in DynamoDB by identity ID. For more information, see Using IAM Policy Conditions for Fine-Grained Access Control in the Amazon DynamoDB Developer Guide.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "dynamodb:GetItem", "dynamodb:BatchGetItem", "dynamodb:Query", "dynamodb:PutItem", "dynamodb:UpdateItem", "dynamodb:DeleteItem", "dynamodb:BatchWriteItem" ], "Resource": [ "arn:aws:dynamodb:us-west-2:123456789012:table/MyTable" ], "Condition": { "ForAllValues:StringEquals": { "dynamodb:LeadingKeys": ["${cognito-identity.amazonaws.com:sub}"] } } } ] }

Grant an identity permission to invoke a Lambda function

The following access policy grants an identity permission to invoke a Lambda function.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "lambda:InvokeFunction", "Resource": [ "arn:aws:lambda:us-west-2:123456789012:function:MyFunction" ] } ] }

Grant an identity permission to publish records to Kinesis Data Streams

The following access policy allows an identity to use the PutRecord operation with any of the Kinesis Data Streams. It can be applied to users that need to add data records to all streams in an account. For more information, see Controlling Access to Amazon Kinesis Data Streams Resources Using IAM in the Amazon Kinesis Data Streams Developer Guide.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "kinesis:PutRecord", "Resource": [ "arn:aws:kinesis:us-east-1:111122223333:stream/stream1" ] } ] }

Grant an identity access to their data in the Amazon Cognito Sync store

The following access policy grants an identity permissions to access only their own data in the Amazon Cognito Sync store.

{ "Version": "2012-10-17", "Statement":[{ "Effect":"Allow", "Action":"cognito-sync:*", "Resource":["arn:aws:cognito-sync:us-east-1:123456789012:identitypool/${cognito-identity.amazonaws.com:aud}/identity/${cognito-identity.amazonaws.com:sub}/*"] }] }