New posts in Http Status Codes

What's the appropriate HTTP status code to return if a user tries logging in with an incorrect username / password, but correct format?

Laravel - Return json along with http status code

what should be HTTP status code for credentials Expired error/exception?

Is it correct to return 404 when a REST resource is not found?

HTTP Status Code for Captcha

Spring: return @ResponseBody "ResponseEntity<List<JSONObject>>"

In a REST API paginated resources: what would you return when a client request a page exceeding the maximum page number?

3rd party API gives back 500 error, what code should my API return

Is there a maximum HTTP status code message length?

Are there languages/software that implements http status code 418?