Openvpn suddenly asking for private key password

After OpenVPN version 2.6.0 the auth mechanism has changed a bit, so clients using a certificate and key that is old, might have a problem where the user is continuosly prompted to enter their "private key password" even if the private key used for the auth does not have a password.

The solution is to add a line to the config file telling openvpn to use the legacy auth mechanism.
Just add the following line in your config file;

providers legacy default

ref:
New OpenVPN 2.6.0 Client (Windows 10 64bit) fails to connect - Virtual Private Networks / OpenVPN - IPFire Community
Suddenly openvpn client asks about private key password. : r/sysadmin
OpenVPN client 2.6.X private key password prompt - Virtual Private Networks / OpenVPN - IPFire Community