To allow Google to index login-required parts of your site, you can create a Google Search Console account and submit a sitemap that includes the URLs of the login-protected pages. You can also use the "Fetch as Google" feature to test the accessibility of these pages by Google.
Additionally, you can consider implementing server-side authentication, such as HTTP authentication, to provide Google with the necessary credentials to access the content of the login-protected pages.
It is also important to note that if the content of the login-protected pages is not publicly accessible, it may not be indexed by Google regardless of the steps taken to allow it.
If you want to allow Google to index login-required parts of your site, you will need to follow a few steps, but keep in mind that this option is not available for all types of content, as Google typically indexes publicly accessible information.
Remember that even if you take these steps, Google may not always index the login-required content, especially if it determines that the content is not relevant or valuable to its users.
It's important to note that allowing Google to index login-required parts of your site may not always be the best solution. If the content is sensitive or not meant for public consumption, it is recommended to keep it behind a login wall for security reasons. Consider evaluating the importance and relevance of the content to determine if it is necessary to make it accessible to search engines.