I am a Raspberry Pi and ESP8266 user.
This is not my final bid. Reasons are as following:
Your job request does not clearly identify what will server do besides authentication. In other words, why people will be registered users. What will they get from this system?
Answer of that question will most likely result in an additional application development on the server.
1- Develop registration system
2- Develop server application to serve registered users
On top of that, you will highly likely require an additional security on your system. That is to keep your registry information safe and server operational.
I would not suggest Raspberry Pi device to be used as a server for following reasons:
- It may get locked. Yes, it sounds weird but it gets locked occasionally under load. I am using it and I do confirm that.
- For some countries, there is small possibility of electricity infrastructure to be interrupted. I know that happened even in Japan in the past.
- When user amount increases, database size will increase, RAM needed for database system will increase. Limited RAM of Raspberry Pi will result file system swapping (writing information in memory to slow performing sd card and deleting that written information in order for application(s) to have available memory)
My suggestion may change depending on answer to my question number 2 above. At the moment I would suggest to rent a VPS system for 1 EURO/month.
I can share my experience over chat if you would like that.