Paypal OAuth2 strategy for Überauth.

1. Setup your application at https://developer.paypal.com.

2. Add :ueberauth_paypal to your list of dependencies in mix.exs:

   def deps do
     [{:ueberauth_paypal, "~> 0.2.0"}]
   end

3. Add the strategy to your applications:

   def application do
     [applications: [:ueberauth_paypal]]
   end

4. Add Paypal to your Überauth configuration:

   config :ueberauth, Ueberauth,
     providers: [
       paypal: {Ueberauth.Strategy.Paypal, []}
     ]

5. Update your provider configuration:

   config :ueberauth,
     Ueberauth.Strategy.Paypal.OAuth, [
       client_id: System.get_env("PAYPAL_CLIENT_ID"),
       client_secret: System.get_env("PAYPAL_CLIENT_SECRET"),
       sandbox: false
     ]

   Note: the sandbox option, in your dev and test you might want to set this to true. The sandbox has different API credentials.

6. Include the Überauth plug in your controller:

   defmodule MyApp.AuthController do
     use MyApp.Web, :controller
     plug Ueberauth
     ...
   end

7. Create the request and callback routes if you haven't already:

   scope "/auth", MyApp do
     pipe_through :browser
   
     get "/:provider", AuthController, :request
     get "/:provider/callback", AuthController, :callback
   end

8. Your controller needs to implement callbacks to deal with Ueberauth.Auth and Ueberauth.Failure responses.

For an example implementation see the Überauth Example application.

Depending on the configured URL you can initialize the request through:

/auth/paypal