HTTP Authorization header field not treated as case-insensitive leading to new editor not working

In 'application/libraries/Api/Rest/Endpoint/EndpointFactory.php'[1], the check for the "Authorization" header field is not case-insensitive, as mandated by the HTTP standard.
Thus, the new editor won't work (i.e. be stuck with "Checking permissions…") when ran behind a http server or proxy that uses lower cases header fields (for example haproxy in HTTP/2 mode, as HTTP/2 requires the conversion of header fields to lower case).

[1] https://github.com/LimeSurvey/LimeSurvey/blob/9e6aa71beb752f11b68f03c33e554c81c71cdddc/application/libraries/Api/Rest/Endpoint/EndpointFactory.php#L232-L238