4: Authentication HTTP handlers

[willemschots]

This PR adds the POST /register endpoint and a supporting types for implementing further HTTP handlers.

Generic handlers

Earlier I wrote a post about generic HTTP handlers, this PR expands on the code from the article by introducing a generic "mapper" with three types of constructor functions:

• mapRequest: maps a HTTP request to target function input.
• mapResponse: maps the result of a target function to a HTTP response.
• mapBoth: maps both of the above.

The mapper allows for functionality to be overwritten when needed, this will be especially handy for mapping responses: For some endpoints we might want to redirect to another URL, while for others we will want to return a 2xx status code and a body.

At the moment input is mapped using the gorilla/schema package. It checks if types implement encoding.TextMarshaler so works pretty well with our custom types.

The code can be found in internal/web/mapper.go. Check it out.

[willemschots]

Note: Linter is failing because of unused code, will be fixed when I implement the other endpoints this weekend :)