asp net web api Authentication token expiration?

Question

I am client of an asp net web API application which uses token based authentication. The token structure is as follows:

{
    access_token: "…",
    token_type: "bearer",
    expires_in: 3599
}

obviously it is set to expire, and I am currently asking for a new token with every request, which i believe not to be a good practice since every API request is actually 2, one for authentication and another for the actual request. So am trying to implement some caching of the token, but i do not know what exactly the expires_in field means, is it seconds, miliseconds?

Answer 1

Looking at oAuth2 protocol spec :

expires_in RECOMMENDED. The lifetime in seconds of the access token. For example, the value "3600" denotes that the access token will expire in one hour from the time the response was generated. If omitted, the authorization server SHOULD provide the expiration time via other means or document the default value.