Authorization plugin about apiclient

[rnkyr]

consider

final class AuthorizationPlugin: PluginType {
    
    private let provider: AuthorizationCredentialsProvider
    
    init(provider: AuthorizationCredentialsProvider) {
        self.provider = provider
    }
    
    func prepare(_ request: APIRequest) -> APIRequest {
        var requestProxy = APIRequestProxy(request: request)
        
        if let request = request as? CredentialProvidableRequest {
            applyHeaders(&requestProxy, applyAuthorization: request.authorizationRequired)
        }
        
        return requestProxy
    }
    
    private func applyHeaders(_ request: inout APIRequestProxy, applyAuthorization: Bool) {
        var headers = request.headers ?? [:]
        
        if applyAuthorization {
            var prefix = ""
            if let authPrefix = provider.authorizationType.valuePrefix {
                prefix = authPrefix + " "
            }
            headers[provider.authorizationType.key] = prefix + provider.authorizationToken
        }
        
        request.headers = headers
    }
}

public protocol AuthorizationCredentialsProvider: class {
    
    var authorizationToken: String { get }
    var authorizationType: AuthType { get }
}