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User Guide

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How AWS Services Work with IAM

Before you use IAM to manage access to AWS services, you should understand what IAM features are available to use. To get a high-level view of how AWS services work with IAM, see AWS Services That Work with IAM in the IAM User Guide.

Identity-Based Policies

With IAM identity-based policies, you can specify allowed or denied actions and resources as well as the conditions under which actions are allowed or denied. To learn about all of the elements that you use in a JSON policy, see IAM JSON Policy Elements Reference in the IAM User Guide.

Actions

The Action element of an IAM identity-based policy describes the specific action or actions that will be allowed or denied by the policy. Policy actions usually have the same name as the associated AWS API operation. The action is used in a policy to grant permissions to perform the associated operation.

Policy actions use a prefix before the action. Policy statements must include either an Action or NotAction element. Each service defines its own set of actions that describe tasks that you can perform with the service.

To specify multiple actions in a single statement, separate them with commas as follows:

"Action": [ "service-prefix:action1", "service-prefix:action2"

You can specify multiple actions using wildcards (*). For example, to specify all actions that begin with the word Describe, include the following action:

"Action": "service-prefix:Describe*"

To see a list of AWS actions, see Actions, Resources, and Condition Keys for AWS Services in the IAM User Guide.

Resources

The Resource element specifies the object or objects to which the action applies. Statements must include either a Resource or a NotResource element. You specify a resource using an ARN or using the wildcard (*) to indicate that the statement applies to all resources.

For more information about the format of ARNs, see Amazon Resource Names (ARNs) and AWS Service Namespaces.

To specify all instances that belong to a specific account, use the wildcard (*):

"Resource": "arn:aws:service-prefix:us-east-1:123456789012:resource-type/*"

Some actions, such as those for creating resources, cannot be performed on a specific resource. In those cases, you must use the wildcard (*).

"Resource": "*"

Some API actions involve multiple resources, so an IAM user must have permissions to use all the resources. To specify multiple resources in a single statement, separate the ARNs with commas.

"Resource": [ "resource1", "resource2"

To learn with which actions you can specify the ARN of each resource, see Actions, Resources, and Condition Keys for AWS Services.

Condition Keys

The Condition element (or Condition block) lets you specify conditions in which a statement is in effect. The Condition element is optional. You can build conditional expressions that use condition operators, such as equals or less than, to match the condition in the policy with values in the request.

If you specify multiple Condition elements in a statement, or multiple keys in a single Condition element, AWS evaluates them using a logical AND operation. If you specify multiple values for a single condition key, AWS evaluates the condition using a logical OR operation. All of the conditions must be met before the statement's permissions are granted.

You can also use placeholder variables when you specify conditions. For example, you can grant an IAM user permission to access a resource only if it is tagged with their IAM user name. For more information, see IAM Policy Elements: Variables and Tags in the IAM User Guide.

To see all AWS global condition keys, see AWS Global Condition Context Keys in the IAM User Guide."

AWS Resource-Based Policies

Resource-based policies are JSON policy documents that specify what actions a specified principal can perform on a resource and under what conditions. Resource-based policies let you grant usage permission to other accounts on a per-resource basis.

To enable cross-account access, you can specify an entire account or IAM entities in another account as the principal in a resource-based policy. Adding a cross-account principal to a resource-based policy is only half of establishing the trust relationship. When the principal and the resource are in different AWS accounts, you must also grant the principal entity permission to access the resource. Grant permission by attaching an identity-based policy to the entity. However, if a resource-based policy grants access to a principal in the same account, no additional identity-based policy is required. For more information, see How IAM Roles Differ from Resource-based Policies in the IAM User Guide.

To view an example of a detailed resource-based policy page, see https://docs.aws.amazon.com/lambda/latest/dg/access-control-resource-based.html.

Authorization Based on Tags

You can attach tags to resources or pass tags in a request. To control access based on tags, you provide tag information in the condition element of a policy using the prefix:ResourceTag/key-name, aws:RequestTag/key-name, or aws:TagKeys condition keys.

To view an example identity-based policy for limiting access to a resource based on the tags on that resource, see Viewing Resources Based on Tags.

IAM Roles

An IAM role is an entity within your AWS account that has specific permissions.

Using Temporary Credentials

You can use temporary credentials to sign in with federation, assume an IAM role, or to assume a cross-account role. You obtain temporary security credentials by calling AWS Security Token Service (AWS STS) API operations such as AssumeRole or GetFederationToken.

Service-Linked Roles

Service-linked roles allow AWS services to access resources in other services to complete an action on your behalf. Service-linked roles appear in your IAM account and are owned by the service. An IAM administrator can view but not edit the permissions for service-linked roles.

Service Roles

This feature allows a service to assume a service role on your behalf. This role allows the service to access resources in other services to complete an action on your behalf. Service roles appear in your IAM account and are owned by the account. This means that an IAM administrator can change the permissions for this role. However, doing so might break the functionality of the service.