I have used ASP.NET Identity for a while now and have been looking at JWT (JSON Web Token) as they seem really interesting and easy to use.
JWT.IO has a great example/to
Unfortunately The previous answer could be misleading: Bearer Tokens are the predominant type of access token used with OAuth 2.0. A Bearer Token is an opaque string, not intended to have any meaning to clients using it. Some servers will issue tokens that are a short string of hexadecimal characters, while others may use structured tokens such as JSON Web Tokens. (https://oauth.net/2/bearer-tokens/)