Hello, my name is Evgeny and I manage a team of 20 Russian Developers based in St. Petersburg.
Your task can be implemented by having one central repository of logins through which user logins are being checked. Like OAuth work now for google, facebook, etc. - similar technology
As for me personally, I managed a software development center for T-mobile in Russia, we had 130 software developers there.
Most of key people now joined me and we have our own venture to provide software development services.
Outside of freelancer.com we have developed about 20 mobile apps (native iOS, Android) for taxi and food delivery services, geolocation, etc. Also we have developed and selling on SAAS basis top web-chat solution for commercial entities. Platform now have about 1 million hits a day.
At freelancer.com we are just for 2 weeks, so started small.
However we have excellent reviews, 100% completion rate and repeat customer projects.
Now we have a couple of 1000$ projects: python, django, Google Apps Script. We would be very happy if you trust us with this project, we are looking for long-term cooperation...