🔒refactor: social login and remove direct user model access in strategies (#2946)

* refactor: checking `ALLOW_SOCIAL_REGISTRATION` with `isEnabled`

* feat: Add findUserByEmail function to UserService

This commit adds a new function, , to the  module. This function retrieves a user document from the database based on the provided email. It returns the user document if found, otherwise it returns null. If there is a problem during user retrieval, an error is thrown.

* refactor: add socialLogin to remove repetitive code

api/strategies/socialLogin.js

@@ -0,0 +1,38 @@
+const { createNewUser, handleExistingUser } = require('./process');
+const { logger } = require('~/config');
+const { findUserByEmail } = require('~/server/services/UserService');
+const { isEnabled } = require('~/server/utils');
+
+const socialLogin =
+  (provider, getProfileDetails) => async (accessToken, refreshToken, profile, cb) => {
+    try {
+      const { email, id, avatarUrl, username, name, emailVerified } = getProfileDetails(profile);
+
+      const oldUser = await findUserByEmail(email);
+      const ALLOW_SOCIAL_REGISTRATION = isEnabled(process.env.ALLOW_SOCIAL_REGISTRATION);
+
+      if (oldUser) {
+        await handleExistingUser(oldUser, avatarUrl);
+        return cb(null, oldUser);
+      }
+
+      if (ALLOW_SOCIAL_REGISTRATION) {
+        const newUser = await createNewUser({
+          email,
+          avatarUrl,
+          provider,
+          providerKey: `${provider}Id`,
+          providerId: id,
+          username,
+          name,
+          emailVerified,
+        });
+        return cb(null, newUser);
+      }
+    } catch (err) {
+      logger.error(`[${provider}Login]`, err);
+      return cb(err);
+    }
+  };
+
+module.exports = socialLogin;