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/currency/chf.json

@@ -1 +1 @@
-{"sections":[],"primaryContentSections":[{"declarations":[{"platforms":["macOS"],"tokens":[{"kind":"keyword","text":"case"},{"kind":"text","text":" "},{"kind":"identifier","text":"CHF"}],"languages":["swift"]}],"kind":"declarations"}],"kind":"symbol","schemaVersion":{"minor":3,"patch":0,"major":0},"metadata":{"title":"Components.Schemas.Currency.CHF","modules":[{"name":"DiscogsService"}],"externalID":"s:14DiscogsService10ComponentsO7SchemasO8CurrencyO3CHFyA2GmF","symbolKind":"case","fragments":[{"kind":"keyword","text":"case"},{"text":" ","kind":"text"},{"text":"CHF","kind":"identifier"}],"role":"symbol","roleHeading":"Case"},"hierarchy":{"paths":[["doc:\/\/DiscogsService\/documentation\/DiscogsService","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/Currency"]]},"variants":[{"traits":[{"interfaceLanguage":"swift"}],"paths":["\/documentation\/discogsservice\/components\/schemas\/currency\/chf"]}],"identifier":{"interfaceLanguage":"swift","url":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/Currency\/CHF"},"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/Currency/CHF":{"abstract":[],"role":"symbol","type":"topic","title":"Components.Schemas.Currency.CHF","fragments":[{"text":"case","kind":"keyword"},{"text":" ","kind":"text"},{"text":"CHF","kind":"identifier"}],"kind":"symbol","url":"\/documentation\/discogsservice\/components\/schemas\/currency\/chf","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/Currency\/CHF"},"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"}]},"doc://DiscogsService/documentation/DiscogsService/Components/Schemas/Currency":{"url":"\/documentation\/discogsservice\/components\/schemas\/currency","type":"topic","title":"Components.Schemas.Currency","abstract":[{"type":"text","text":"A list of currency codes defined in the marketplace."}],"kind":"symbol","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/Currency","fragments":[{"text":"enum","kind":"keyword"},{"kind":"text","text":" "},{"kind":"identifier","text":"Currency"}],"role":"symbol","navigatorTitle":[{"text":"Currency","kind":"identifier"}]}}}
+{"metadata":{"fragments":[{"text":"case","kind":"keyword"},{"text":" ","kind":"text"},{"text":"CHF","kind":"identifier"}],"symbolKind":"case","modules":[{"name":"DiscogsService"}],"title":"Components.Schemas.Currency.CHF","role":"symbol","roleHeading":"Case","externalID":"s:14DiscogsService10ComponentsO7SchemasO8CurrencyO3CHFyA2GmF"},"identifier":{"interfaceLanguage":"swift","url":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/Currency\/CHF"},"schemaVersion":{"major":0,"patch":0,"minor":3},"hierarchy":{"paths":[["doc:\/\/DiscogsService\/documentation\/DiscogsService","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas","doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/Currency"]]},"primaryContentSections":[{"declarations":[{"languages":["swift"],"platforms":["macOS"],"tokens":[{"text":"case","kind":"keyword"},{"text":" ","kind":"text"},{"text":"CHF","kind":"identifier"}]}],"kind":"declarations"}],"variants":[{"paths":["\/documentation\/discogsservice\/components\/schemas\/currency\/chf"],"traits":[{"interfaceLanguage":"swift"}]}],"sections":[],"kind":"symbol","references":{"doc://DiscogsService/documentation/DiscogsService/Components/Schemas/Currency":{"identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/Currency","role":"symbol","title":"Components.Schemas.Currency","navigatorTitle":[{"kind":"identifier","text":"Currency"}],"url":"\/documentation\/discogsservice\/components\/schemas\/currency","fragments":[{"kind":"keyword","text":"enum"},{"kind":"text","text":" "},{"kind":"identifier","text":"Currency"}],"abstract":[{"text":"A list of currency codes defined in the marketplace.","type":"text"}],"kind":"symbol","type":"topic"},"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"}]},"doc://DiscogsService/documentation/DiscogsService/Components/Schemas/Currency/CHF":{"title":"Components.Schemas.Currency.CHF","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService\/Components\/Schemas\/Currency\/CHF","abstract":[],"type":"topic","fragments":[{"text":"case","kind":"keyword"},{"text":" ","kind":"text"},{"text":"CHF","kind":"identifier"}],"role":"symbol","url":"\/documentation\/discogsservice\/components\/schemas\/currency\/chf","kind":"symbol"},"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":{"role":"collection","title":"DiscogsService","kind":"symbol","identifier":"doc:\/\/DiscogsService\/documentation\/DiscogsService","abstract":[],"type":"topic","url":"\/documentation\/discogsservice"}}}