# Control access for invoking an API
In this section, you learn about the permissions model for controlling access to your API using IAM permissions. When IAM authorization is enabled, clients must use Signature Version 4a (SigV4a) and Signature Version 4 (SigV4) to sign their requests with AWS credentials. For more information, see [AWS Signature Version 4](https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_sigv.html).
In this section, we show a template IAM policy statement and the policy statement reference. The policy statement reference includes the formats of `Action` and `Resource` fields related to the API execution service. Use these references to create your IAM policy statement. When you create your IAM policy statement, you might need to consider the how API Gateway resource policies affect the authorization workflow. For more information, see [How API Gateway resource policies affect authorization workflow](apigateway-authorization-flow.md).
For private APIs, you should use a combination of an API Gateway resource policy and a VPC endpoint policy. For more information, see the following topics:
+ [Control access to a REST API with API Gateway resource policies](apigateway-resource-policies.md)
+ [Use VPC endpoint policies for private APIs in API Gateway](apigateway-vpc-endpoint-policies.md)
## Control who can call an API Gateway API method with IAM policies
To control who can or cannot call a deployed API with IAM permissions, create an IAM policy document with required permissions. A template for such a policy document is shown as follows.
------
#### [ JSON ]
****
```
{
"Version":"2012-10-17",
"Statement": [
{
"Effect": "Permission",
"Action": [
"execute-api:Execution-operation"
],
"Resource": [
"arn:aws:execute-api:region:123456789012:api-id/stage/METHOD_HTTP_VERB/Resource-path"
]
}
]
}
```
------
Here, `Permission` is to be replaced by `Allow` or `Deny` depending on whether you want to grant or revoke the included permissions. `Execution-operation` is to be replaced by the operations supported by the API execution service. `METHOD_HTTP_VERB` stands for a HTTP verb supported by the specified resources. `Resource-path` is the placeholder for the URL path of a deployed API `[Resource](https://docs.aws.amazon.com/apigateway/latest/api/API_Resource.html)` instance supporting the said `METHOD_HTTP_VERB`. For more information, see [Statement reference of IAM policies for executing API in API Gateway](#api-gateway-calling-api-permissions).
**Note**
For IAM policies to be effective, you must have enabled IAM authentication on API methods by setting `AWS_IAM` for the methods' `[authorizationType](https://docs.aws.amazon.com/apigateway/latest/api/API_Method.html#authorizationType)` property. Failing to do so will make these API methods publicly accessible.
For example, to grant a user permission to view a list of pets exposed by a specified API, but to deny the user permission to add a pet to the list, you could include the following statement in the IAM policy:
------
#### [ JSON ]
****
```
{
"Version":"2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"execute-api:Invoke"
],
"Resource": [
"arn:aws:execute-api:us-east-1:111111111111:api-id/*/GET/pets"
]
},
{
"Effect": "Deny",
"Action": [
"execute-api:Invoke"
],
"Resource": [
"arn:aws:execute-api:us-east-1:111111111111:api-id/*/POST/pets"
]
}
]
}
```
------
To grant a user permission to view a specific pet exposed by an API that is configured as `GET /pets/{petId}`, you could include the following statement in the IAM policy:
------
#### [ JSON ]
****
```
{
"Version":"2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"execute-api:Invoke"
],
"Resource": [
"arn:aws:execute-api:us-east-1:111122223333:api-id/*/GET/pets/a1b2"
]
}
]
}
```
------
## Statement reference of IAM policies for executing API in API Gateway
The following information describes the Action and Resource format of IAM policy statements of access permissions for executing an API.
### Action format of permissions for executing API in API Gateway
The API-executing `Action` expression has the following general format:
```
execute-api:action
```
where *action* is an available API-executing action:
+ **\$1**, which represents all of the following actions.
+ **Invoke**, used to invoke an API upon a client request.
+ **InvalidateCache**, used to invalidate API cache upon a client request.
### Resource format of permissions for executing API in API Gateway
The API-executing `Resource` expression has the following general format:
```
arn:aws:execute-api:region:account-id:api-id/stage-name/HTTP-VERB/resource-path-specifier
```
where:
+ *region* is the AWS region (such as **us-east-1** or **\$1** for all AWS regions) that corresponds to the deployed API for the method.
+ *account-id* is the 12-digit AWS account Id of the REST API owner.
+ *api-id* is the identifier API Gateway has assigned to the API for the method.
+ *stage-name* is the name of the stage associated with the method.
+ *HTTP-VERB* is the HTTP verb for the method. It can be one of the following: GET, POST, PUT, DELETE, PATCH.
+ *resource-path-specifier* is the path to the desired method.
**Note**
If you specify a wildcard (`*`), the `Resource` expression applies the wildcard to the rest of the expression.
Some example resource expressions include:
+ **arn:aws:execute-api:\$1:\$1:\$1** for any resource path in any stage, for any API in any AWS region.
+ **arn:aws:execute-api:us-east-1:\$1:\$1** for any resource path in any stage, for any API in the AWS region of `us-east-1`.
+ **arn:aws:execute-api:us-east-1:\$1:*api-id*/\$1** for any resource path in any stage, for the API with the identifier of *api-id* in the AWS region of us-east-1.
+ **arn:aws:execute-api:us-east-1:\$1:*api-id*/`test`/\$1** for any resource path in the stage of `test`, for the API with the identifier of *api-id* in the AWS region of us-east-1.
To learn more, see [API Gateway Amazon Resource Name (ARN) reference](arn-format-reference.md).