TODO List

Improvement of path matcher
More flexible option for rewriting path
Refactoring

Split backend module into three parts
- backend(s): struct containing info, defined for each served domain with multiple paths
- upstream/upstream group: information on targeted destinations for each set of (a domain + a path)
- load-balance: load balancing mod for a domain + path
Unit tests
Options to serve custom http_error page.
Prometheus metrics
Documentation
Client certificate
- support intermediate certificate. Currently, only supports client certificates directly signed by root CA.
- Currently, we took the following approach (caveats)
  - For Http2 and 1.1, prepare rustls::ServerConfig for each domain name and hence client CA cert is set for each one.
  - For Http3, use aggregated rustls::ServerConfig for multiple domain names except for ones requiring client-auth. So, if a domain name is set with client authentication, http3 doesn't work for the domain.
Make the session-persistance option for load-balancing sophisticated. (mostly done in v0.3.0)
- add option for sticky cookie name
- add option for sticky cookie duration
etc.