Use the fingerprint to validate the certificate manually!
In most cases, certificate is signed by a trusted Certificate Authority (CA).
It can be: An SSL certificate is automatically trusted by standard Subversion clients and web-browsers if it's signed by a trusted Certificate Authority.
If cached, Subversion will automatically trust this certificate in future negotiations.
Many Open SSL installations also have a pre-defined set of “default” CAs that are nearly universally trusted.
To make the Subversion client automatically trust these standard authorities, set the ssl-trust-default-ca variable to true.