How to Get Function this token.?

Hallo can somebody help for get function this token from POST DATA …

utf8=%E2%9C%93&authenticity_token=P2GI2cf%2Z8Q3uIQVZ55ZOH2%2EzqD8jGk6zM80XVh1NAawzRG2SM1Xteay8X8NUqlCLlpU4FYHqJlBccVB5QJVQg4%3D%3D&user%5Blogin%5D=&user%5Bpassword%5D=&user%5Bremember_me%5D=1&commit=Masuk

You just look for it in the previous requests, usually u can find it in previous source, and sometimes it can be in the headers or cookies