# How Amazon IoT Greengrass works with IAM
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Before you use IAM to manage access to Amazon IoT Greengrass, you should understand the IAM features that you can use with Amazon IoT Greengrass.


| IAM feature | Supported by Greengrass? | 
| --- | --- | 
| [Identity-based policies with resource-level permissions](#security_iam_service-with-iam-id-based-policies) | Yes | 
| [Resource-based policies](#security_iam_service-with-iam-resource-based-policies) | No | 
| [Access control lists (ACLs)](#security_iam_service-with-iam-acls) | No | 
| [Tags-based authorization](#security_iam_service-with-iam-tags) | Yes | 
| [Temporary credentials](#security_iam_service-with-iam-roles-tempcreds) | Yes | 
| [Service-linked roles](#security_iam_service-with-iam-roles-service-linked) | No | 
| [Service roles](#security_iam_service-with-iam-roles-service-linked) | Yes | 

For a high-level view of how other Amazon services work with IAM, see [Amazon services that work with IAM](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_aws-services-that-work-with-iam.html) in the *IAM User Guide*.

## Identity-based policies for Amazon IoT Greengrass
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With IAM identity-based policies, you can specify allowed or denied actions and resources and the conditions under which actions are allowed or denied. Amazon IoT Greengrass supports specific actions, resources, and condition keys. To learn about all of the elements that you use in a policy, see [IAM JSON policy elements reference](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_elements.html) in the *IAM User Guide*.

### Actions
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Administrators can use Amazon JSON policies to specify who has access to what. That is, which **principal** can perform **actions** on what **resources**, and under what **conditions**.

The `Action` element of a JSON policy describes the actions that you can use to allow or deny access in a policy. Include actions in a policy to grant permissions to perform the associated operation.

Policy actions for Amazon IoT Greengrass use the `greengrass:` prefix before the action. For example, to allow someone to use the `ListCoreDevices` API operation to list the core devices in their Amazon Web Services account, you include the `greengrass:ListCoreDevices` action in their policy. Policy statements must include either an `Action` or `NotAction` element. Amazon IoT Greengrass defines its own set of actions that describe tasks that you can perform with this service.

To specify multiple actions in a single statement, list them between brackets (`[` `]`) and separate them with commas, as follows:

```
"Action": [
  "greengrass:{{action1}}",
  "greengrass:{{action2}}",
  "greengrass:{{action3}}"
]
```

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

```
"Action": "greengrass:List*"
```

**Note**  
We recommend that you avoid the use of wildcards to specify all available actions for a service. As a best practice, you should grant least privilege and narrowly scope permissions in a policy. For more information, see [Grant minimum possible permissions](security-best-practices.md#least-privilege).

For the complete list of Amazon IoT Greengrass actions, see [Actions Defined by Amazon IoT Greengrass](https://docs.amazonaws.cn/IAM/latest/UserGuide/list_awsiotgreengrass.html#awsiotgreengrass-actions-as-permissions) in the *IAM User Guide*.

### Resources
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Administrators can use Amazon JSON policies to specify who has access to what. That is, which **principal** can perform **actions** on what **resources**, and under what **conditions**.

The `Resource` JSON policy element specifies the object or objects to which the action applies. As a best practice, specify a resource using its [Amazon Resource Name (ARN)](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference-arns.html). For actions that don't support resource-level permissions, use a wildcard (\*) to indicate that the statement applies to all resources.

```
"Resource": "*"
```

The following table contains the Amazon IoT Greengrass resource ARNs that can be used in the `Resource` element of a policy statement. For a mapping of supported resource-level permissions for Amazon IoT Greengrass actions, see [Actions Defined by Amazon IoT Greengrass](https://docs.amazonaws.cn/IAM/latest/UserGuide/list_awsiotgreengrass.html#awsiotgreengrass-actions-as-permissions) in the *IAM User Guide*.

Some Amazon IoT Greengrass actions (for example, some list operations), cannot be performed on a specific resource. In those cases, you must use the wildcard alone.

```
"Resource": "*"
```

To specify multiple resource ARNs in a statement, list them between brackets (`[` `]`) and separate them with commas, as follows:

```
"Resource": [
  "{{resource-arn1}}",
  "{{resource-arn2}}",
  "{{resource-arn3}}"
]
```

For more information about ARN formats, see [Amazon Resource Names (ARNs) and Amazon service namespaces](https://docs.aws.amazon.com/general/latest/gr/aws-arns-and-namespaces.html) in the *Amazon Web Services General Reference*.

### Condition keys
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Administrators can use Amazon JSON policies to specify who has access to what. That is, which **principal** can perform **actions** on what **resources**, and under what **conditions**.

The `Condition` element specifies when statements execute based on defined criteria. You can create conditional expressions that use [condition operators](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_elements_condition_operators.html), such as equals or less than, to match the condition in the policy with values in the request. To see all Amazon global condition keys, see [Amazon global condition context keys](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_condition-keys.html) in the *IAM User Guide*.

### Examples
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To view examples of Amazon IoT Greengrass identity-based policies, see [Identity-based policy examples for Amazon IoT Greengrass](security_iam_id-based-policy-examples.md).

## Resource-based policies for Amazon IoT Greengrass
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Amazon IoT Greengrass does not support [resource-based policies](security-iam.md#security_iam_access-manage-resource-based-policies).

## Access control lists (ACLs)
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Amazon IoT Greengrass does not support [ACLs](security-iam.md#security_iam_access-manage-acl).

## Authorization based on Amazon IoT Greengrass tags
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You can attach tags to supported Amazon IoT Greengrass resources or pass tags in a request to Amazon IoT Greengrass. To control access based on tags, you provide tag information in the [Condition element](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_elements_condition.html) of a policy using the `aws:ResourceTag/${TagKey}`, `aws:RequestTag/${TagKey}`, or `aws:TagKeys` condition keys. For more information, see [Tag your Amazon IoT Greengrass Version 2 resources](tag-resources.md).

## IAM roles for Amazon IoT Greengrass
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An [IAM role](https://docs.amazonaws.cn/IAM/latest/UserGuide/id_roles.html) is an entity within your Amazon Web Services account that has specific permissions.

### Using temporary credentials with Amazon IoT Greengrass
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Temporary credentials are used to sign in with federation, assume an IAM role, or to assume a cross-account role. You obtain temporary security credentials by calling Amazon STS API operations such as [AssumeRole](https://docs.amazonaws.cn/STS/latest/APIReference/API_AssumeRole.html) or [GetFederationToken](https://docs.amazonaws.cn/STS/latest/APIReference/API_GetFederationToken.html).

On the Greengrass core, temporary credentials for the [device role](device-service-role.md) are made available to Greengrass components. If your components use the Amazon SDK, you don't need to add logic to obtain the credentials because the Amazon SDK does this for you.

### Service-linked roles
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Amazon IoT Greengrass does not support [service-linked roles](https://docs.amazonaws.cn/IAM/latest/UserGuide/id_roles_terms-and-concepts.html#iam-term-service-linked-role).

### Service roles
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This feature allows a service to assume a [service role](https://docs.amazonaws.cn/IAM/latest/UserGuide/id_roles_terms-and-concepts.html#iam-term-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.

Amazon IoT Greengrass core devices use a service role to allow Greengrass components and Lambda functions to access some of your Amazon resources on your behalf. For more information, see [Authorize core devices to interact with Amazon services](device-service-role.md).

Amazon IoT Greengrass uses a service role to access some of your Amazon resources on your behalf. For more information, see [Greengrass service role](greengrass-service-role.md).