Conditional INSERT

Hello,

I want to insert data into table only if condition is true.
For example:

INSERT into  mytable (domainid, hostname, txtdata)
  VALUES (100,'_acme.challenge.example', 'somedata');

The insert should only be done if Hostname like %_acme.challenge%.

How can it be done? I dont want that the user/script can insert any value.

Best regards.