api: add github oauth

Closes https://gitlab.com/commento/commento/issues/20

api/oauth_github.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/github"
+	"os"
+)
+
+var githubConfig *oauth2.Config
+
+func githubOauthConfigure() error {
+	githubConfig = nil
+	if os.Getenv("GITHUB_KEY") == "" && os.Getenv("GITHUB_SECRET") == "" {
+		return nil
+	}
+
+	if os.Getenv("GITHUB_KEY") == "" {
+		logger.Errorf("COMMENTO_GITHUB_KEY not configured, but COMMENTO_GITHUB_SECRET is set")
+		return errorOauthMisconfigured
+	}
+
+	if os.Getenv("GITHUB_SECRET") == "" {
+		logger.Errorf("COMMENTO_GITHUB_SECRET not configured, but COMMENTO_GITHUB_KEY is set")
+		return errorOauthMisconfigured
+	}
+
+	logger.Infof("loading github OAuth config")
+
+	githubConfig = &oauth2.Config{
+		RedirectURL:  os.Getenv("ORIGIN") + "/api/oauth/github/callback",
+		ClientID:     os.Getenv("GITHUB_KEY"),
+		ClientSecret: os.Getenv("GITHUB_SECRET"),
+		Scopes: []string{
+			"read:user",
+			"user:email",
+		},
+		Endpoint: github.Endpoint,
+	}
+
+	configuredOauths = append(configuredOauths, "github")
+
+	return nil
+}