OAuth 2.0 BCP -> OAuth 2.1

[n2ygk]

Is your feature request related to a problem? Please describe.

The OAuth 2.0 Security Best Current Practice draft describes a number of best security practices and the OAuth 2.1 draft consolidates all the OAuth 2.0 RFCs and BCPs into a single document.

DOT is not in compliance with all the BCPs.

Describe the solution you'd like

Review these BCPs and update DOT as appropriate.

This will likely require deprecating some features and adding others.

Describe alternatives you've considered

Additional context