prioritize access_token URL param over Authorization header

go 1.18; modules

make all UserAgent checks case-insensitive (#4)

* Handle alternate case for docker and Go user-agents

Some docker instances are unable to login through Beyond. That's because the user-agent is spelled with a D instead of a d.
Examples of these user-agents include:
- Docker-Client/20.10.7 (darwin)
- Docker-Client/nerdctl-v0.12.1 (linux)

* Update to use ToLower

Co-authored-by: LeoChen <lchen@cogolabs.com>

fixup GitHub bearer tokens

add home URL flag

Update README.md

add SAML session mapping flag

add SAML signing method setting

add all SAML NameID formats

cleanup OIDC flags vs. SAML