Cannot select the signature key correctly when the Authentication subkey exists

[dingwen07]

When performing signature operations, if the public key provided contains a GnuPG Authentication subkey (key purpose is Authentication only), the signature operation will always try to use the Authentication subkey instead of other subkeys defined for the purpose of signing. This will cause the signature be invalid and could not be verified.

The following Issue is related. https://github.com/trustcrypto/OnlyKey-App/issues/148

[dingwen07]

If I remove the "Authentication" subkey from my key and provide the public key to WebCrypt, Signing will work.