[v2] Document providers

Thanks to @LoriKarikari (who has provided most of these) and node-oauth (by @ciaranj) we have a rapidly growing list of supported providers.

What they are and how to pass in your own need to be documented somewhere, in addition to the README (docs/providers.mdx?)

Currently Supported

• Discord
• GitHub
• Google
• Mixer
• Slack
• Twitter
• Twitch

Planned

• Reddit (in PR)
• Facebook

In addition, support for the following ‘built in’ providers (which can be enabled/disabled) is also planned, although they may not drop at the same time.

• Email (e.g. via sign in link) - Either in v2.0 or v2.1 (TBD)
• Credentials (e.g. email + password, 2FA, etc) - Likely to drop in v2.1 or later

These were both supported in v1, but only email sign in was supported out of the box and the token / email verification system could have been better.

[LoriKarikari]

I came across this nodemailer page and it says you can configure with only the provider name. Is that an option too?

[LoriKarikari]

I’m currently documenting but I’m stuck at the email provider. In your example app, you are using EMAIL_SERVER which is a connection string but when I look at the provider file itself it has this config:

server: {
    host: 'localhost',
    port: 25,
    auth: {
     user: '',
     pass: ''
    }
},

I haven’t looked through all the commits yet but has it changed? Edit: okay, I see you edited it 😉