Release v21.6.0

Added

• TenancyOptions.BaseDomain, configured through UseSubdomainTenancy(baseDomain, fallbackHeaderName) (#2471)
• TenancyOptionsValidator, which validates tenancy configuration while the host starts (#2471)

Changed

• Subdomain tenancy resolves a tenant only for a host that sits below the configured base domain, and falls back to the tenant header for anything else — an apex domain, a deeper host, or an address (#2471)
• A host is matched case-insensitively and in punycode form, so one domain is always one tenant regardless of how it was written (#2471)
• A resolved tenant must be a valid DNS label, so a host cannot put a wildcard, user information, a control character or an unbounded string into a tenant identifier (#2471)

Fixed

• An apex domain no longer resolves to a tenant named after the site (#2471)
• An IPv4 or IPv6 literal is no longer read as a tenant, in any spelling (#2471)
• IHttpRequestContext.Host no longer truncates an IPv6 literal to its opening bracket (#2471)

Removed

• The UseSubdomainTenancy(fallbackHeaderName) overload — subdomain tenancy now requires a base domain, and the header name is the second argument (#2471)

Security

• Subdomain tenancy configured without a valid base domain now fails at startup, instead of resolving no tenant from any host and falling back to a client-supplied header that selects the namespace and database (#2471)