Improve documentation for "encoding" parameter in REST interface

[Vampire]

I tried to get client-side hashing via the "REST Interface" to work.
I had a hard time (in the end reading the source code) to find out, that I have to give data base64 encoded and addtionally set encoding to BASE64.
I just got as error, that the supplied data length does not match the hash algorithm expected length.
After I have set encoding to BASE64 it started working.
But the only places where it is mentioned is in doc/htdocs/REST_Interface.html as possible request parameter.
But it is nowhere really described and completely missing e.g. from https://docs.keyfactor.com/signserver/latest/plain-signer and https://docs.keyfactor.com/signserver/latest/client-side-hashing.

I think it would be very beneficial to add some words about it to the documentation.

[netmackan]

This is a parameter in the REST interface so it would not fit on the client-side-hashing page. The authoritative source for it should be in the OpenAPI spec but there currently it is only given with an example of encoding=NONE. The other place is on the REST interface page where as you say it is only mentioned as a possible parameter.

Two improvements could be made:

• Specify it more clearly in the OpenAPI spec both with explanation about what it is and with its possible values
• On the REST interface page also explain it there and/or include an example for it

[netmackan]

The REST documentation is getting a major overhaul including getting examples (both cURL and Postman) for most endpoints.