The issue isn't the config, but the fact that crypt() doesn't have any way to signal failure. In better designed languages you would have exceptions, result types, or something. Even in C you have "return integer indicating success or error" which would've prevented the confusion.

Now the public API is hard to change but you could still avoid the issue by returning a longer token like "==DANGEROUS_CRYPT_ERROR_length==" or "==DANGEROUS_CRYPT_ERROR_unsupported_alg==" which would never match the password field unless someone was really trying to induce the issue.