refactor: oauth flow (#726)

* wip

* feat: add oauth session impl in auth service

* feat: move oauth logic into auth service and handle multiple sessions

* tests: fix tests

* fix: review comments

* fix: prevent ddos attacks in oauth rate limit

internal/service/oauth_presets.go

@@ -0,0 +1,23 @@
+package service
+
+import (
+	"github.com/steveiliop56/tinyauth/internal/config"
+	"golang.org/x/oauth2/endpoints"
+)
+
+func newGoogleOAuthService(config config.OAuthServiceConfig) *OAuthService {
+	scopes := []string{"openid", "email", "profile"}
+	config.Scopes = scopes
+	config.AuthURL = endpoints.Google.AuthURL
+	config.TokenURL = endpoints.Google.TokenURL
+	config.UserinfoURL = "https://openidconnect.googleapis.com/v1/userinfo"
+	return NewOAuthService(config)
+}
+
+func newGitHubOAuthService(config config.OAuthServiceConfig) *OAuthService {
+	scopes := []string{"read:user", "user:email"}
+	config.Scopes = scopes
+	config.AuthURL = endpoints.GitHub.AuthURL
+	config.TokenURL = endpoints.GitHub.TokenURL
+	return NewOAuthService(config).WithUserinfoExtractor(githubExtractor)
+}