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 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
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.
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
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.
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.
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.
Services that unauthenticated enhanced flow users can access
Category | Service |
---|---|
Analytics |
Amazon Kinesis Data Firehose Amazon Kinesis Data Analytics |
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 |
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 |
Neworking & Content Delivery |
Amazon API Gateway |
Security, Identity, & Compliance |
Amazon Cognito Identity Amazon Cognito user pools Amazon Cognito Sync |
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 |
|
To grant access to Services that
unauthenticated enhanced flow users can access, 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 eliminate that service from your use case or switch to
the basic flow.
Access policy examples
In this section, you can find example Amazon Cognito access policies that grant only
the permissions your identities must complete a 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
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 permissions 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}/*"] }] }