Build our own external login provider about stamhoofd

[SimonBackx]

Related to #57

[WardToulet]

This sounds great but a lot of additional work and maybe a bit out of the scope of stamhoofds core functionality, are you planning on doing this as a speparate but related project to stamhoofd or are your planning of adding it entierly into the existing codebase?

[SimonBackx]

Yes, this probably is a bit of extra work. But I'm already planning to release an app, so we could build it into that app.

But I'm not certain this would be a good solution. Having this system will also have downsides. I think a better solution for now would be to have a PWA on Android, and ask for an app install when the registration is complete. So the chance is higher those users will keep signed in (because we can ask for permanent storage when a PWA is installed on Android). We could do the same for iOS, but I really hope Apple introduces better PWA support (and installation) in the future. Currently it is a bit awkward, but if we explain it with some steps I think most users will follow the instructions. Having an app for every organization is certainly the way to go, but not possible with App Stores.