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
Note
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.
-
An
aud
claim of the identity pool IDus-west-2:abcdefg-1234-5678-910a-0e8443553f95
. -
An
amr
claim ofauthenticated
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.
cognito-identity.amazonaws.com:aud
-
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. cognito-identity.amazonaws.com:amr
-
Restricts the role to either
authenticated
orunauthenticated
(guest) users. Amazon Cognito indicates the authentication state in theamr
claim in the identity pool token. cognito-identity.amazonaws.com:sub
-
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 thesub
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.
Note
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.
-
Your user's identity ID.
-
The ARN of the IAM role that your user wants to assume.
-
A
policy
parameter that adds an inline session policy. -
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 |
---|---|
Analytics |
Amazon Data Firehose Amazon Managed Service for Apache Flink |
Application Integration |
Amazon Simple Queue Service |
AR & VR |
Amazon Sumerian¹ |
Business Applications |
Amazon Mobile Analytics Amazon Simple Email Service |
Compute |
AWS Lambda |
Cryptography & PKI |
AWS Key Management Service¹ |
Database |
Amazon DynamoDB Amazon SimpleDB |
Front-end Web & Mobile |
AWS AppSync Amazon Location Service Amazon Simple Notification Service Amazon Pinpoint Amazon Location Service |
Game Development |
Amazon GameLift |
Internet of Things (IoT) |
AWS 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 |
Storage |
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 |
|
Amazon Location Service |
|
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 for guest users
Amazon Cognito first applies an inline policy in the request for IAM credentials. 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. For an overview of the net effect of the inline policy and other session policies, see Services that unauthenticated users can access.
{ "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 for guests
Amazon Cognito also applies an AWS managed policy as a session policy to the
enhanced-flow sessions of unauthenticated guests. This policy limits the scope
of unauthenticated users' permissions with the policy
AmazonCognitoUnAuthedIdentitiesSessionPolicy
.
You must also grant this permission in the policies that you attach to your unauthenticated IAM role. A user's effective permissions for an assumed-role session are the intersection of the IAM policies assigned to their role, and their session policies. For more information, see Session policies in the AWS Identity and Access Management User Guide.
For an overview of the net effect of this AWS managed policy and other session policies, see Services that unauthenticated users can access.
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", "geo:GetMap*", "geo:SearchPlaceIndex*", "geo:GetPlace", "geo:CalculateRoute*", "geo:*Geofence", "geo:*Geofences", "geo:*DevicePosition*" ], "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
Note
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}/*"] }] }