This patch adds new CTAP2 vendor command with command value 0x50. The
command arguments are credentialId and user specified SHA256 hash. It
returns a DER encoded signature of the given hash, using the key
which corresponds to the specified credentialId.

Example request:
{1: <sha256_hash>,
 2: {"id": <credential_id>, "type": "public-key"},
 3: [pinAuth]}

Example response:
{1: <der_signature>}

Issue: solokeys#395

…ith support for arbitrary-length hashes up to 64B and a trusted comment in the EdDSA case.

Also fixed existing bug: get_credential_id_size(SH.cred.type) should be get_credential_id_size(&SH.cred)
Also now cose_alg is checked. I'm not sure yet if it is safe to use arbitrary-length hashes with verify_pin_auth_ex. Maybe a min length should be set?

…ID prefix

…nature algorithm is supported