Implemented the Authentication middleware (#3)

This PR contains the work done to implement the `AuthMiddleware` middleware, to authenticate the requests sent to the backend service, based on [their specifications](https://www.discogs.com/developers/#page:authentication).

In addition, some documentation has been added/updated and some boilerplate source code has been removed from the project.

Reviewed-on: #3
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

docs/data/documentation/discogsservice/components/schemas/serviceerror/message.json

@@ -1 +1 @@
-{"kind":"symbol","hierarchy":{"paths":[["doc:\/\/DiscogsService\/documentation\/DiscogsService","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/ServiceError"]]},"variants":[{"traits":[{"interfaceLanguage":"swift"}],"paths":["\/documentation\/discogsservice\/components\/schemas\/serviceerror\/message"]}],"identifier":{"url":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/ServiceError\/message","interfaceLanguage":"swift"},"abstract":[{"text":"A message of a service error.","type":"text"}],"metadata":{"title":"message","modules":[{"name":"DiscogsService"}],"externalID":"s:14DiscogsService10ComponentsO7SchemasO0B5ErrorV7messageSSvp","symbolKind":"property","fragments":[{"text":"var","kind":"keyword"},{"text":" ","kind":"text"},{"text":"message","kind":"identifier"},{"text":": ","kind":"text"},{"text":"String","kind":"typeIdentifier","preciseIdentifier":"s:SS"}],"role":"symbol","roleHeading":"Instance Property"},"sections":[],"schemaVersion":{"patch":0,"major":0,"minor":3},"primaryContentSections":[{"declarations":[{"languages":["swift"],"tokens":[{"text":"var","kind":"keyword"},{"kind":"text","text":" "},{"text":"message","kind":"identifier"},{"kind":"text","text":": "},{"text":"String","preciseIdentifier":"s:SS","kind":"typeIdentifier"}],"platforms":["macOS"]}],"kind":"declarations"},{"kind":"content","content":[{"level":2,"text":"Discussion","type":"heading","anchor":"discussion"},{"name":"Remark","style":"note","type":"aside","content":[{"type":"paragraph","inlineContent":[{"type":"text","text":"Generated from "},{"type":"codeVoice","code":"#\/components\/schemas\/ServiceError\/message"},{"type":"text","text":"."}]}]}]}],"references":{"doc://DiscogsService/documentation/DiscogsService/Components":{"type":"topic","url":"\/documentation\/discogsservice\/components","role":"symbol","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components","kind":"symbol","title":"Components","navigatorTitle":[{"text":"Components","kind":"identifier"}],"abstract":[{"text":"Types generated from the components section of the OpenAPI document.","type":"text"}],"fragments":[{"kind":"keyword","text":"enum"},{"text":" ","kind":"text"},{"kind":"identifier","text":"Components"}]},"doc://DiscogsService/documentation/DiscogsService/Components/Schemas/ServiceError":{"fragments":[{"kind":"keyword","text":"struct"},{"kind":"text","text":" "},{"kind":"identifier","text":"ServiceError"}],"type":"topic","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/ServiceError","navigatorTitle":[{"kind":"identifier","text":"ServiceError"}],"title":"Components.Schemas.ServiceError","role":"symbol","abstract":[{"type":"text","text":"A type that contains any error data."}],"kind":"symbol","url":"\/documentation\/discogsservice\/components\/schemas\/serviceerror"},"doc://DiscogsService/documentation/DiscogsService/Components/Schemas/ServiceError/message":{"kind":"symbol","title":"message","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/ServiceError\/message","url":"\/documentation\/discogsservice\/components\/schemas\/serviceerror\/message","abstract":[{"text":"A message of a service error.","type":"text"}],"type":"topic","fragments":[{"text":"var","kind":"keyword"},{"text":" ","kind":"text"},{"text":"message","kind":"identifier"},{"text":": ","kind":"text"},{"text":"String","kind":"typeIdentifier","preciseIdentifier":"s:SS"}],"role":"symbol"},"doc://DiscogsService/documentation/DiscogsService":{"url":"\/documentation\/discogsservice","abstract":[],"identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService","kind":"symbol","role":"collection","type":"topic","title":"DiscogsService"},"doc://DiscogsService/documentation/DiscogsService/Components/Schemas":{"identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas","type":"topic","url":"\/documentation\/discogsservice\/components\/schemas","abstract":[{"type":"text","text":"Types generated from the "},{"code":"#\/components\/schemas","type":"codeVoice"},{"type":"text","text":" section of the OpenAPI document."}],"role":"symbol","kind":"symbol","navigatorTitle":[{"text":"Schemas","kind":"identifier"}],"title":"Components.Schemas","fragments":[{"text":"enum","kind":"keyword"},{"text":" ","kind":"text"},{"text":"Schemas","kind":"identifier"}]}}}
+{"kind":"symbol","hierarchy":{"paths":[["doc:\/\/DiscogsService\/documentation\/DiscogsService","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/ServiceError"]]},"abstract":[{"type":"text","text":"A message of a service error."}],"variants":[{"traits":[{"interfaceLanguage":"swift"}],"paths":["\/documentation\/discogsservice\/components\/schemas\/serviceerror\/message"]}],"primaryContentSections":[{"kind":"declarations","declarations":[{"languages":["swift"],"tokens":[{"kind":"keyword","text":"var"},{"kind":"text","text":" "},{"kind":"identifier","text":"message"},{"kind":"text","text":": "},{"preciseIdentifier":"s:SS","kind":"typeIdentifier","text":"String"}],"platforms":["macOS"]}]},{"kind":"content","content":[{"level":2,"anchor":"discussion","type":"heading","text":"Discussion"},{"type":"aside","content":[{"type":"paragraph","inlineContent":[{"type":"text","text":"Generated from "},{"type":"codeVoice","code":"#\/components\/schemas\/ServiceError\/message"},{"type":"text","text":"."}]}],"name":"Remark","style":"note"}]}],"identifier":{"url":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/ServiceError\/message","interfaceLanguage":"swift"},"schemaVersion":{"patch":0,"minor":3,"major":0},"sections":[],"metadata":{"roleHeading":"Instance Property","role":"symbol","externalID":"s:14DiscogsService10ComponentsO7SchemasO0B5ErrorV7messageSSvp","fragments":[{"kind":"keyword","text":"var"},{"kind":"text","text":" "},{"kind":"identifier","text":"message"},{"kind":"text","text":": "},{"preciseIdentifier":"s:SS","kind":"typeIdentifier","text":"String"}],"title":"message","modules":[{"name":"DiscogsService"}],"symbolKind":"property"},"references":{"doc://DiscogsService/documentation/DiscogsService":{"role":"collection","title":"DiscogsService","kind":"symbol","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService","abstract":[],"type":"topic","url":"\/documentation\/discogsservice"},"doc://DiscogsService/documentation/DiscogsService/Components":{"title":"Components","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components","navigatorTitle":[{"text":"Components","kind":"identifier"}],"abstract":[{"type":"text","text":"Types generated from the components section of the OpenAPI document."}],"type":"topic","fragments":[{"text":"enum","kind":"keyword"},{"text":" ","kind":"text"},{"text":"Components","kind":"identifier"}],"role":"symbol","url":"\/documentation\/discogsservice\/components","kind":"symbol"},"doc://DiscogsService/documentation/DiscogsService/Components/Schemas/ServiceError/message":{"kind":"symbol","role":"symbol","url":"\/documentation\/discogsservice\/components\/schemas\/serviceerror\/message","title":"message","fragments":[{"kind":"keyword","text":"var"},{"kind":"text","text":" "},{"kind":"identifier","text":"message"},{"kind":"text","text":": "},{"kind":"typeIdentifier","preciseIdentifier":"s:SS","text":"String"}],"abstract":[{"text":"A message of a service error.","type":"text"}],"type":"topic","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/ServiceError\/message"},"doc://DiscogsService/documentation/DiscogsService/Components/Schemas/ServiceError":{"abstract":[{"text":"A type that contains any error data.","type":"text"}],"fragments":[{"kind":"keyword","text":"struct"},{"text":" ","kind":"text"},{"kind":"identifier","text":"ServiceError"}],"url":"\/documentation\/discogsservice\/components\/schemas\/serviceerror","title":"Components.Schemas.ServiceError","role":"symbol","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/ServiceError","kind":"symbol","type":"topic","navigatorTitle":[{"text":"ServiceError","kind":"identifier"}]},"doc://DiscogsService/documentation/DiscogsService/Components/Schemas":{"role":"symbol","type":"topic","abstract":[{"type":"text","text":"Types generated from the "},{"code":"#\/components\/schemas","type":"codeVoice"},{"text":" section of the OpenAPI document.","type":"text"}],"kind":"symbol","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas","url":"\/documentation\/discogsservice\/components\/schemas","navigatorTitle":[{"text":"Schemas","kind":"identifier"}],"title":"Components.Schemas","fragments":[{"text":"enum","kind":"keyword"},{"text":" ","kind":"text"},{"text":"Schemas","kind":"identifier"}]}}}