# Making an API Request

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

#### Request URI

A request URI consists of the following:

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

Although a request URI is included in a request header, most programming languages or frameworks require the request URI to be separately transmitted, rather than being conveyed in a request message.

Table 1 Parameters in a URI
Parameter | Description
--- | ---
URI-scheme | Protocol used to transmit requests. All APIs use HTTPS.
Endpoint | Domain name or IP address of the server bearing the REST service. The endpoint varies between services in different regions. It can be obtained from Regions and 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.

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.
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:

#### Request Header

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

Table 3 lists common request header fields.

Table 3 Common request headers
Name | Description | Mandatory | Example
--- | --- | --- | ---
Host | Specifies the requested server information, which can be obtained from the URL of the service API. The value is in the hostname[:port] format. If the port number is not specified, the default port is used. The default port number for https is 443. | No This parameter is mandatory for AK/SK authentication. | code.test.com or code.test.com:443
Content-Type | Specifies the MIME type of the request body. You are advised to use the default value application/json. For APIs used to upload objects or images, the value can vary depending on the flow type. | Yes | application/json
Content-Length | Specifies the length of the request body. The unit is byte. | No | 3495
X-Project-Id | Specifies the project ID. Obtain the project ID by following the instructions in Obtaining a Project ID. | No | e9993fc787d94b6c886cbaa340f9c0f4

X-Auth-Token

Specifies the user token.

The user token is a response to the API used to obtain a user token. This API is the only one that does not require authentication.

After the request is processed, the value of X-Subject-Token in the message header is the token value.

No

This parameter is mandatory for token authentication.

The following is part of an example token:

MIIPAgYJKoZIhvcNAQcCo...ggg1BBIINPXsidG9rZ

The API used to obtain a user token does not require authentication. Therefore, only the Content-Type field needs to be added to requests for calling the API. An example of such requests is as follows:

#### (Optional) Request Body

This part is optional. The body of a request is often sent in a structured format (for example, JSON or XML) as specified in the Content-Type header field. If the request body contains Chinese characters, these characters must be coded 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.

In the case of the API 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 username, domainname, ******** (login password), and xxxxxxxxxxxxxxxxxx (project name) with actual values. You can obtain the values from Regions and Endpoints.

The scope parameter specifies where a token takes effect. 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.

    Content-Type: application/json

    {
        "auth": {
            "identity": {
                "methods": [
                    "password"
                ],
                "password": {
                    "user": {
                        "name": "username",
                        "password": "********",
                        "domain": {
                            "name": "domainname"
                        }
                    }
                }
            },
            "scope": {
                "project": {
                    "name": "xxxxxxxxxxxxxxxxxx"
                }
            }
        }
    }

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