# Making an API Request

This section describes the structure of a REST API request, and uses the IAM API for obtaining a user token as an example to demonstrate how to call an API. The obtained token can then be used to authenticate the calling of other APIs.

#### Request URI

The format of a request URI is as follows:

{URI-scheme} :// {Endpoint} / {resource-path} ? {query-string}

Table 1 Request URI
Parameter | Description
--- | ---
URI-scheme | Protocol used to transmit requests. All APIs use HTTPS.
Endpoint | Domain name or IP address of the server for the REST service endpoint. The endpoint varies depending on services in different regions. It can be obtained in Endpoints.
resource-path | Access path of an API for performing a specified operation. Obtain the path from the URI of an API. For example, the resource-path of the API used to obtain a user token is /v3/auth/tokens.
query-string | Query parameter, which is optional. Ensure that a question mark (?) is included before each query parameter that is in the format of "Parameter name=Parameter value". For example, ? limit=10 indicates that a maximum of 10 data records will be displayed.

For example, to obtain an IAM token in a region, obtain the endpoint of IAM for this region and the resource-path (/v3/auth/tokens) in the URI of the API used to obtain a user token. Then, construct the URI as follows:

    https://{iam-endpoint}/v3/auth/tokens

To simplify the URI display in this document, each API is provided only with a resource-path and a request method. The URI-scheme of all APIs is HTTPS, and the endpoints of all APIs in the same region are identical.

#### Request Methods

The HTTP protocol defines the following request methods that can be used to send a request to the server:

Table 2 HTTP methods
Method | Description
--- | ---
GET | Requests the server to return specified resources.
PUT | Requests the server to update specified resources.
POST | Requests the server to add resources or perform special operations.
DELETE | Requests the server to delete specified resources, for example, an object.
HEAD | Same as GET except that the server must return only the response header.
PATCH | Requests the server to update partial content of a specified resource. If the resource does not exist, a new resource will be created.

For example, in the case of the API used to obtain a user token, the request method is POST. The request is as follows:

    POST https://{iam-endpoint}/v3/auth/tokens

#### Request Header

You can also add additional header fields to a request, such as the fields required by a specified URI or HTTP method. For example, to request for the authentication information, add Content-Type, which specifies the request body type.

Table 3 describes the common request header fields to be added to the request.

Table 3 Common request header fields
Header | Description | Mandatory | Example
--- | --- | --- | ---
Content-type | Request body type or format. The default value is application/json. | Yes | application/json
Content-Length | Length of the request body. The unit is byte. | Mandatory for POST and PUT requests but must be left blank for GET requests | 3495
X-Project-Id | Project ID. This parameter is used to obtain the token for each project. | No | e9993fc787d94b6c886cbaa340f9c0f4
X-Auth-Token | User token. It is a response to the API used to obtain a user token. This API is the only one that does not require authentication. | Mandatory for token-based authentication | None
X-Sdk-Date | Time when the request is sent. The time is in YYYYMMDD'T'HHMMSS'Z' format. The value is the current Greenwich Mean Time (GMT) time of the system. | Mandatory for AK/SK-based authentication, optional for PKI token-based authentication | 20190307T101459Z

Authorization

Authentication information.

The value is obtained from the request signature result and is required when the AK/SK are used to encrypt the signature.

Type: string

Default value: none

Mandatory for AK/SK-based authentication

SDK-HMAC-SHA256 Credential=ZIRRKMTWPTQFQI1WKNKB/20150907//ec2/sdk_request, SignedHeaders=content-type;host;x-sdk-date, Signature=55741b610f3c9fa3ae40b5a8021ebf7ebc2a28a603fc62d25cb3bfe6608e1994

Host | Information about the requested server. The value can be obtained from the URL of the service API. This value is host name[:port number]. If the port number is not specified, the default port is used. The default port number for https is 443. | Mandatory for AK/SK-based authentication | code.test.com or code.test.com:443

In addition to supporting authentication using tokens, APIs support authentication using AK/SK, which uses SDK to sign a request. During the signature, the Authorization (signature authentication) and X-Sdk-Date (time when a request is sent) headers are automatically added to the request.

The API for obtaining a user token does not require authentication. Therefore, this API only requires adding the Content-Type field. The request with the added Content-Type header is as follows:

    POST https://{iam-endpoint}/v3/auth/tokens
    Content-Type: application/json

#### Request Body

The body of a request is often sent in a structured format as specified in the Content-Type header field. The request body transfers content except the request header. If the request body contains Chinese characters, these characters must be encoded in UTF-8.

The request body varies between APIs. Some APIs do not require the request body, such as the APIs requested using the GET and DELETE methods.

If an API is used to obtain a user token, the request parameters and parameter description can be obtained from the API request. The following provides an example request with a body included. Replace user_name, domain_name, and user_password with the actual username, account name, and login password, respectively. project_name is the project name. For details, see Obtaining a Username and ID, Obtaining an Account Name and ID, and Obtaining a Project ID.

The scope parameter specifies where a token takes effect. In the example, the token takes effect only for the resources in a specified project. ModelArts uses a region-specific endpoint to call this API. Set scope to project. You can set scope to an account or a project under an account. In the following example, the token takes effect only for the resources in a specified project. For more information about this API, see "Obtaining a User Token".

    POST https://{iam-endpoint}/v3/auth/tokens
    Content-Type:application/json
    {
      "auth": {
        "identity": {
          "methods": ["password"],
          "password": {
            "user": {
              "name": "Username",
              "password": "User password",
              "domain": {
                "name": "Domain name"
              }
            }
          }
        },
        "scope": {
          "project": {
            "name": "Project name"
          }
        }
      }
    }

If all data required for the API request is available, you can send the request to call the API through curl, Postman, or coding. In the response to the API used to obtain a user token, x-subject-token is the desired user token. This token can then be used to authenticate the calling of other APIs.

Parent topic: Calling APIs