Execution Order for the ApiController

Assuming the request goes into the ApiController scope, the operation order is as below:

The ExecuteAsync method of the ApiController is invoked.
The Initialize method of the ApiController is invoked.
The registered Action Selector is retrieved.
The SelectAction method of the registered action selector is invoked. If only one action method is matched, the pipeline continues.
All registered Filters for the selected action is retrieved.
The Authorization Filters are called. The authorization filter can decide either to let the pipeline to continue executing or to terminate the pipeline.
If Authorization Filters didn't terminate the request, action parameter bindings are performed.
ApiController.ModelState is set.
Action Filters are invoked. The Action Filters can decide either to let the pipeline to continue executing or terminate the pipeline.
If Action Filters didn't terminate the request, registered Action Invoker is retrieved.
The InvokeActionAsync method of the registered Action Invoker is called to invoked the selected action method.
Note: If any exception occurs from the execution of the Authorization Filters to the execution of the action method, the exception filters are be called.

There are a few more things which happen in between but this is very close to a complete view. Check out the ApiController source code for more information.

2019-02-25 16:16:17.668+08:00 INFO [59]: CustomMessageHandler.SendAsync
2019-02-25 16:16:18.107+08:00 INFO [59]: BaseApiController.Initialize