Crypto-Agility: support keys beyond RSA #349

Our federation has signing keys for RSA, ECDSA, ML-DSA and SLH-DSA. With pyFF 3.0.0's updated dependencies on the Python cryptography library, signing documents with all four comes into reach.

The config file does not seem to have options to specify the type of key; one simply points to the key and cert files.

A first test however shows that it's failing so far, with different reasons given for ECDSA vs. PQC algorithms:

ECDSA key:

pyff.pipes:Got exception when loading/executing pipe: key error: unable to auto-detect key format from PEM data

ML-DSA and SLH-DSA keys:

pyff.pipes:Got exception when loading/executing pipe: key error: key type does not match algorithm RsaPkcs1v15(Sha256)

I can contribute towards test cases (updated scripts/genkey.sh to generate all four variants, if that is seen as helpful.