I currently use Mozilla Persona to auth 50k users, with at least 15k sign-in events per month over 300 websites.<p>The biggest problems with login box, a.k.a. drov.io:<p>1) Trust. Who are you?<p>2) Pricing. Even with 300 sites, 1,000 concurrent users at any given moment, and fully dynamic sites, the proposed pricing for me of EUR 70 per month is a quarter of all my current costs. The cloud has made things very cheap, and this looks very expensive as a result.<p>3) Multi-user and PaaS. How could I grant access to the membership and management of one slice of users but not the rest? i.e. my 300 sites are on one platform, each site is typically a non-profit who own their own users... in theory they own their user database and I just host it, they should be able to manage it and for me to query that to apply authorisation within my app.<p>4) Longevity. If I consider moving things over... what happens in 18 months time if you reach the end of your runway? How could I reverse adopting this?<p>5) How do I identify a user? Assuming you auth them and then say &quot;you&#x27;re good&quot;, what single thing can I use to identify them that is meaningful to me? Persona returns a verified email for all users, are you able to do the same?<p>6) Are you static site friendly? i.e. Can the pages with the &quot;Sign-in&quot; box be cached and thus allow me to serve great numbers with little hardware, and does loading a page with a &quot;Sign-in&quot; box always trigger a HTTP request to you (if I&#x27;m under DDoS attack, is it going to take you down?)<p>7) How do you manage &quot;email change&quot;? Or things like &quot;I signed in with my Gmail, but now I want to use my Github&quot;?<p>Those things weigh heavily. Happy to talk with you about them, I notice that you&#x27;re in London and so am I. These sites are side projects, not my main gig... just things that linger and that I still maintain.