For many sites that have customer or client portals, including SaaS companies, the login page is the primary destination for a lot of searchers. It will help your customers bypass your homepage and go right to the login area. The question asked of Google is how do you ensure that login page shows up as a Sitelink in your Google Search results snippet.
The short answer is that there is no way to guarantee it but there are things you can do to help influence Google there.
John Mueller from Google spoke about this at the 12:35 mark in the last Google office hours video. He said, you need to make sure that the login page has some content on the page and that the login page is accessible to search engines.
What John did not mention is how to maybe help encourage Google to show specific links there, you may want to have those links in your main navigation on your site (mobile site). Although, John didn’t specifically say that. He said in the past that sometimes flat architecture sites have issues with Sitelinks…
So here are the sitelinks for my site:
I do not see my client login link page as a sitelink:
I honestly do not want it to be a sitelink, but if I did, I’d probably make sure that is a primary link on the mobile version of my site and that I’d add more content to that page.