Function type for callback when username and/or password is required.
Should update the NULL terminated strings in the username and/or
password buffers.
@param userdata The user data for the callback.
@param host The host description (typically "<hostname>:<port>").
@param username A buffer of size usize, possibly containing a NULL
terminated default username.
@param usize The size of the username buffer.
@param password A buffer of size psize, possibly containing a NULL
terminated default password.
@param psize The size of the password buffer.
@return 0 on success, -1 on error (errno should be set).
Function type for callback when username and/or password is required.
Should update the NULL terminated strings in the username and/or password buffers.
@param userdata The user data for the callback. @param host The host description (typically "<hostname>:<port>"). @param username A buffer of size usize, possibly containing a NULL terminated default username. @param usize The size of the username buffer. @param password A buffer of size psize, possibly containing a NULL terminated default password. @param psize The size of the password buffer. @return 0 on success, -1 on error (errno should be set).