Support for simplified DNS configuration for service discovery

[Ingemārs Ašmanis]

To simplify DNS configuration and make service discovery faster we have changed preferred way to configure your authentication service domain. 

Legacy configuration (PTR - > SRV -> A):

_notakey2._tcp.example.com.      IN PTR main._notakey2._tcp.example.com.
main._notakey2._tcp.example.com. IN SRV 1 10 443 mfa.example.com.
mfa.example.com.                 IN A   192.168.1.128

Current configuration example, (PTR no longer required):

_notakey2._tcp.example.com.  IN  SRV 1 10 443 mfa.example.com.
mfa.example.com.             IN  A   192.168.1.128

SRV record can contain multiple service records with different priorities:   

_notakey2._tcp.example.com.  IN  SRV 1 10 443 mfa1.example.com.
_notakey2._tcp.example.com.  IN  SRV 1 20 443 mfa2.example.com.
mfa1.example.com.            IN  A   192.168.1.128

mfa2.example.com.            IN  A   192.168.1.129

Client application support: 

iOS >= 2.4.69 

Android >= 2.4.41

The legacy DNS configuration will remain valid until further notice, but comes with penalty of slight delay of single additional DNS lookup for PTR record.