# Authentication

Requests for calling an API can be authenticated using either of the following methods:

- Token-based authentication: Requests are authenticated using a token.
- AK/SK-based authentication: Requests are authenticated by encrypting the request body using an AK/SK pair.

#### Token-based Authentication

The validity period of a token is 24 hours. When using a token for authentication, cache it to prevent frequently calling the IAM API used to obtain a user token.

A token specifies temporary permissions in a computer system. During API authentication using a token, the token is added to request headers to get permissions for calling the API.

You can obtain a token by calling the API described in Obtaining a User Token. IAM APIs can be called only by using a global service token. To call the API described in Obtaining a User Token, set auth.scope to domain in the request body as follows:

    {
        "auth": {
            "identity": {
                "methods": [
                    "password"
                ],
                "password": {
                    "user": {
                        "domain": {
                            "name": "IAMDomain"
                        },
                        "name": "IAMUser",
                        "password": "IAMPassword"
                    }
                }
            },
            "scope": {
                "domain": {
                    "name": "IAMDomain"
                }
            }
        }
    }

After a token is obtained, the X-Auth-Token header field must be added to requests to specify the token when calling other APIs. For example, if the token is ABCDEFJ...., X-Auth-Token: ABCDEFJ.... can be added to a request as follows:

#### AK/SK-based Authentication

AK/SK-based authentication supports API requests with a body not larger than 12 MB. For API requests with a larger body, token-based authentication is recommended.

In AK/SK-based authentication, AK/SK is used to sign requests and the signature is then added to the requests for authentication.

- AK: access key ID, which is a unique identifier used in conjunction with a secret access key to sign requests cryptographically.
- SK: secret access key used in conjunction with an AK to sign requests cryptographically. It identifies a request sender and prevents the request from being modified.

In AK/SK-based authentication, you can use an AK/SK pair to sign requests based on the signature algorithm or use the signing SDK to sign requests.

The signing SDK is only used for signing requests and is different from the SDKs provided by services.

Parent topic: Calling APIs