api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/oauth_google.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/google"
+	"os"
+)
+
+var googleConfig *oauth2.Config
+
+func googleOauthConfigure() error {
+	googleConfig = nil
+	if os.Getenv("GOOGLE_KEY") == "" && os.Getenv("GOOGLE_SECRET") == "" {
+		return nil
+	}
+
+	if os.Getenv("GOOGLE_KEY") == "" {
+		logger.Errorf("GOOGLE_KEY not configured, but GOOGLE_SECRET is set")
+		return errorOauthMisconfigured
+	}
+
+	if os.Getenv("GOOGLE_SECRET") == "" {
+		logger.Errorf("GOOGLE_SECRET not configured, but GOOGLE_KEY is set")
+		return errorOauthMisconfigured
+	}
+
+	logger.Infof("loading Google OAuth config")
+
+	googleConfig = &oauth2.Config{
+		RedirectURL:  os.Getenv("BACKEND_WEB") + "/oauth/google/callback",
+		ClientID:     os.Getenv("GOOGLE_KEY"),
+		ClientSecret: os.Getenv("GOOGLE_SECRET"),
+		Scopes: []string{
+			"https://www.googleapis.com/auth/userinfo.profile",
+			"https://www.googleapis.com/auth/userinfo.email",
+		},
+		Endpoint: google.Endpoint,
+	}
+
+	return nil
+}