# Functions
NewVpnClient returns new vpn client.
SetDefaultLogger is to set logger for vpn client.
WithAuthMethod returns OptionFunc for inserting auth method.
WithGRPCInsecure returns OptionFunc for inserting grpc insecure.
WithSelfSignedCertification returns OptionFunc for inserting grpc custom certification.
WithServerAddr returns OptionFunc for inserting server addr.
WithServerPort returns OptionFunc for inserting server port.
# Type aliases
OptionFunc is a function for Option interface.