# How Amazon Transfer Family works with IAM
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Before you use Amazon Identity and Access Management (IAM) to manage access to Amazon Transfer Family, you should understand what IAM features are available to use with Amazon Transfer Family. To get a high-level view of how Amazon Transfer Family and 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*.

**Topics**
+ [Amazon Transfer Family identity-based policies](#security_iam_service-with-iam-id-based-policies)
+ [Amazon Transfer Family resource-based policies](#security_iam_service-with-iam-resource-based-policies)
+ [Authorization based on Amazon Transfer Family tags](#security_iam_service-with-iam-tags)
+ [Amazon Transfer Family IAM roles](#security_iam_service-with-iam-roles)

## Amazon Transfer Family identity-based policies
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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. Amazon Transfer Family supports specific actions, resources, and condition keys. To learn about all of the elements that you use in a JSON policy, see [IAM JSON policy elements reference](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_elements.html) in the *Amazon Identity and Access Management 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 in Amazon Transfer Family use the following prefix before the action: `transfer:`. For example, to grant someone permission to create a server, with the Transfer Family `CreateServer` API operation, you include the `transfer:CreateServer` action in their policy. Policy statements must include either an `Action` or `NotAction` element. Amazon Transfer Family defines its own set of actions that describe tasks that you can perform with this service.

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

```
"Action": [
      "transfer:action1",
      "transfer:action2"
```

You can specify multiple actions using wildcards (\$1). For example, to specify all actions that begin with the word `Describe`, include the following action.

```
"Action": "transfer:Describe*"
```

To see a list of Amazon Transfer Family actions, see [Actions defined by Amazon Transfer Family](https://docs.amazonaws.cn/service-authorization/latest/reference/list_awstransferfamily.html#awstransferfamily-actions-as-permissions) in the *Service Authorization Reference*.

### 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 (\$1) to indicate that the statement applies to all resources.

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

The Transfer Family server resource has the following ARN.

```
arn:aws-cn:transfer:${Region}:${Account}:server/${ServerId}
```

For example, to specify the `s-01234567890abcdef` Transfer Family server in your statement, use the following ARN.

```
"Resource": "arn:aws-cn:transfer:us-east-1:123456789012:server/s-01234567890abcdef"
```

For more information about the format of ARNs, see [Amazon Resource Names (ARNs)](https://docs.amazonaws.cn/general/latest/gr/aws-arns-and-namespaces.html) in the *Service Authorization Reference*, or [IAM ARNs](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_identifiers.html#identifiers-arns) in the *IAM User Guide*.

To specify all instances that belong to a specific account, use the wildcard (\$1).

```
"Resource": "arn:aws-cn:transfer:us-east-1:123456789012:server/*"
```

Some Amazon Transfer Family actions are performed on multiple resources, such as those used in IAM policies. In those cases, you must use the wildcard (\$1).

```
"Resource": "arn:aws-cn:transfer:*:123456789012:server/*"
```

In some cases you need to specify more than one type of resource, for example, if you create a policy that allows access to Transfer Family servers and users. To specify multiple resources in a single statement, separate the ARNs with commas.

```
"Resource": [
      "resource1",
      "resource2"
            ]
```

To see a list of Amazon Transfer Family resources, see [Resource types defined by Amazon Transfer Family](https://docs.amazonaws.cn/service-authorization/latest/reference/list_awstransferfamily.html#awstransferfamily-resources-for-iam-policies) in the *Service Authorization 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*.

Amazon Transfer Family defines its own set of condition keys and also supports using some global condition keys. To see a list of Amazon Transfer Family condition keys, see [Condition keys for Amazon Transfer Family](https://docs.amazonaws.cn/service-authorization/latest/reference/list_awstransferfamily.html#awstransferfamily-policy-keys) in the *Service Authorization Reference*.

### Examples
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To view examples of Amazon Transfer Family identity-based policies, see [Amazon Transfer Family identity-based policy examples](security_iam_id-based-policy-examples.md). For VPC endpoint-specific IAM policies, see [Limiting VPC endpoint access for Transfer Family servers](create-server-in-vpc.md#limit-vpc-endpoint-access).

## Amazon Transfer Family resource-based policies
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Resource-based policies are JSON policy documents that specify what actions a specified principal can perform on the Amazon Transfer Family resource and under what conditions. Amazon S3 supports resource-based permissions policies for Amazon S3 *buckets*. Resource-based policies let you grant usage permission to other accounts on a per-resource basis. You can also use a resource-based policy to allow an Amazon service to access your Amazon S3 *buckets*.

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](https://docs.amazonaws.cn/IAM/latest/UserGuide/reference_policies_elements_principal.html). 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 Amazon 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 ](https://docs.amazonaws.cn/IAM/latest/UserGuide/id_roles_compare-resource-policies.html)in the *Amazon Identity and Access Management User Guide*.

The Amazon S3 service supports only one type of resource-based policy called a **bucket* policy*, which is attached to a *bucket*. This policy defines which principal entities (accounts, users, roles, and federated users) can perform actions on the object.

### Examples
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To view examples of Amazon Transfer Family resource-based policies, see [Amazon Transfer Family tag-based policy examples](security_iam_tag-based-policy-examples.md).

## Authorization based on Amazon Transfer Family tags
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You can attach tags to Amazon Transfer Family resources or pass tags in a request to Amazon Transfer Family. 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 `transfer:ResourceTag/key-name`, `aws:RequestTag/key-name`, or `aws:TagKeys` condition keys. For information about how to use tags to control access to Amazon Transfer Family resources, see [Amazon Transfer Family tag-based policy examples](security_iam_tag-based-policy-examples.md).

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

### Using temporary credentials with Amazon Transfer Family
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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 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).

Amazon Transfer Family supports using temporary credentials.