Refactor CSRF protection modules, make sure CSRF tokens can be up-to-date. (#19337)

Do a refactoring to the CSRF related code, remove most unnecessary functions.
Parse the generated token's issue time, regenerate the token every a few minutes.

routers/web/auth/auth.go

@@ -345,7 +345,7 @@ func handleSignInFull(ctx *context.Context, u *user_model.User, remember, obeyRe
 		ctx.Locale = middleware.Locale(ctx.Resp, ctx.Req)
 	}
 
-	// Clear whatever CSRF has right now, force to generate a new one
+	// Clear whatever CSRF cookie has right now, force to generate a new one
 	middleware.DeleteCSRFCookie(ctx.Resp)
 
 	// Register last login

routers/web/auth/oauth.go

@@ -1007,7 +1007,7 @@ func handleOAuth2SignIn(ctx *context.Context, source *auth.Source, u *user_model
 			log.Error("Error storing session: %v", err)
 		}
 
-		// Clear whatever CSRF has right now, force to generate a new one
+		// Clear whatever CSRF cookie has right now, force to generate a new one
 		middleware.DeleteCSRFCookie(ctx.Resp)
 
 		// Register last login