Sending authorization header to http input plugin

I am using http input plugin to send an http request from postman with "Authorization" header but apparently logstash is not reading this header name

when i try to display headers field, "Authorization" header is not displayed

but if i change it to anything else like "authorization_header" the header is being read and displayed

Could anyone tell me the reason for this?

I am using logstash 7.6.1

Here is the configuration :

        input {

              http {

                port => "5043"

              }

        }

        filter {

                ruby {

                    code => "puts 'request headers : ';

                            puts event.get('headers')"

                }
        }

        output {

                elasticsearch {

                    hosts => ["${ELASTICSEARCH_HOST}:${ELASTICSEARCH_PORT}"]

                    index => "test_index"

                }
        }