feat: Multiple Type-Safe Authentication Methods

[Andrew-Lees11]

Description

Added a new protocol TypeSafeMultiCredentials. A user can create a final class or struct that conforms to this protocol to add authentication to a route with multiple authentication methods. The user defines an array of TypeSafeCredentials and then this class will iterate through the array trying to authenticate. When one the authentications is successful the users type will initialize an instance of itself which is passed to the route handler.

Example of usage:

public struct MultiAuthedUser : TypeSafeMultiCredentials {

    public let id: String
    public let provider: String
    public let name: String?

    public static var authenticationMethods: [TypeSafeCredentials.Type] = [BasicAuthedUser.self, TokenAuthedUser.self]

    public init(successfulAuth: TypeSafeCredentials) {
        // Initialize common attributes of an authenticated user
        self.id = successfulAuth.id
        self.provider = successfulAuth.provider
        // Initialize extended attributes that depend on the type of authentication
        switch(successAuth.self) {
        case let tokenProfile as TokenAuthedUser:
            self.name = tokenProfile.name
        default:
            self.name = nil
        }
    }
}

router.get("/multiauth") { (userProfile: MultiAuthedUser, respondWith: (MultiAuthedUser?, RequestError?) -> Void) in
    print("authenticated \(userProfile.id) using \(userProfile.provider)")
    respondWith(userProfile, nil)
}

[codecov-io]

Codecov Report

Merging #68 into master will increase coverage by 8.73%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #68      +/-   ##
==========================================
+ Coverage   58.15%   66.89%   +8.73%     
==========================================
  Files           6        7       +1     
  Lines         282      293      +11     
==========================================
+ Hits          164      196      +32     
+ Misses        118       97      -21

Flag	Coverage Δ
#Credentials	66.89% <100%> (+8.73%)	⬆️

Impacted Files	Coverage Δ
Sources/Credentials/TypeSafeCredentials.swift	67.74% <ø> (+67.74%)	⬆️
Sources/Credentials/MultiTypeSafeCredentials.swift	100% <100%> (ø)

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[djones6]

Looks good, but I think we might want to tweak the example for init(successfulAuth:) a bit (see comments below)

[djones6]

This could be rewritten to initialize self.id and self.provider before the switch, and then initialize the more specific fields (in this case self.name) within each case.

[djones6]

In this example you are not initializing self.name in the default case - I presume that means it's an optional which takes an implicit nil value? It might be nicer for the example to explicitly set self.name = nil in the default case.

[djones6]

Should this be AuthedUser (or SingleAuthedUser) to be consistent with the multi-auth example below?