Foursquare

• Foursquare.swift
• https://developer.foursquare.com/overview/auth

// Client-side (implicit) flow
let foursquare: Provider = .Foursquare(
    clientID: "***",
    redirectURL: "foo://callback"
)

// Server-side (explicit) flow
let foursquare: Provider = .Foursquare(
    clientID: "***",
    clientSecret: "***"
    redirectURL: "foo://callback"
)