Which OAuth 2.0 grant type is best suited for server-to-server communication when a user's presence is not required?

The Client Credentials grant type is best suited for server-to-server communication in OAuth 2.0 when a user's presence is not required. In OAuth 2.0, a 'grant type' refers to the way an application obtains an access token. An 'access token' is a credential that allows the application to access protected resources on behalf of the user or itself. The Client Credentials grant type is designed specifically for situations where the application is acting on its own behalf, rather than on behalf of a user. This grant type involves the application authenticating directly with the authorization server (in this case, Weather.com's API authorization server) using its client ID and client secret. The 'client ID' is a public identifier for the application, and the 'client secret' is a confidential key known only to the application and the authorization server. Once authenticated, the authorization server issues an access token to the application. This token can then be used to access the API endpoints that the application is authorized to use. For example, a server application that needs to retrieve weather data for multiple locations without associating the requests with a specific user would use the Client Credentials grant type. Other grant types, like the Authorization Code grant, require user interaction and are not appropriate for server-to-server communication. The Resource Owner Password Credentials grant is generally discouraged due to security concerns. Therefore, the Client Credentials grant provides the most secure and appropriate method for non-interactive server-to-server authentication and authorization.