Add HTTP core: Faraday connection, error mapping, response wrapper, pagination, and OAuth2

lib/fiken/oauth.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+require "uri"
+require "faraday"
+
+module Fiken
+  # OAuth2 authorization-code helper.
+  #
+  #   oauth = Fiken::OAuth.new(client_id:, client_secret:, redirect_uri:)
+  #   redirect_to oauth.authorize_url(state: "abc")
+  #   token = oauth.exchange_code(params[:code])
+  #   client = Fiken::Client.new(access_token: token.access_token)
+  #   refreshed = oauth.refresh(token.refresh_token)
+  class OAuth
+    AUTHORIZE_URL = "https://fiken.no/oauth/authorize"
+    TOKEN_URL = "https://fiken.no/oauth/token"
+
+    attr_reader :client_id, :client_secret, :redirect_uri
+
+    def initialize(client_id:, client_secret:, redirect_uri: nil)
+      @client_id = client_id
+      @client_secret = client_secret
+      @redirect_uri = redirect_uri
+    end
+
+    # Build the URL to send the user to in order to authorize the app.
+    def authorize_url(state:, redirect_uri: self.redirect_uri, scope: nil)
+      params = {
+        response_type: "code",
+        client_id: client_id,
+        redirect_uri: redirect_uri,
+        state: state,
+        scope: scope
+      }.compact
+      "#{AUTHORIZE_URL}?#{URI.encode_www_form(params)}"
+    end
+
+    # Exchange the authorization code from the callback for tokens.
+    def exchange_code(code, redirect_uri: self.redirect_uri)
+      token_request(grant_type: "authorization_code", code: code, redirect_uri: redirect_uri)
+    end
+
+    # Use a refresh token to obtain a fresh access token.
+    def refresh(refresh_token)
+      token_request(grant_type: "refresh_token", refresh_token: refresh_token)
+    end
+
+    private
+
+    def token_request(params)
+      response = token_connection.post(TOKEN_URL, params.compact)
+      raise Error.from_response(response.status, response.body) if response.status >= 400
+
+      Object.new(response.body)
+    end
+
+    def token_connection
+      @token_connection ||= Faraday.new do |f|
+        f.request :url_encoded
+        f.request :authorization, :basic, client_id, client_secret
+        f.response :json, content_type: /\bjson$/
+        f.adapter Faraday.default_adapter
+      end
+    end
+  end
+end