decode_with_jwks failing when alg missing

The published MSFT JWKs don't include the alg value which according to the RFC is optional. This causes token.decode_with_jwks(&jwkset) to always fail here:

biscuit/src/jws.rs

Lines 164 to 167 in 2cbe6ed

    
           let algorithm = match jwk.common.algorithm { 
        
               Some(Algorithm::Signature(algorithm)) => algorithm, 
        
               _ => Err(ValidationError::UnsupportedKeyAlgorithm)?, 
        
           };

Since the field is optional, something like this works to check it if the value is present.

If you'd accept this as a PR let me know

Sure. Please submit a PR.

	let algorithm = match jwk.common.algorithm {
	Some(Algorithm::Signature(algorithm)) => algorithm,
	_ => Err(ValidationError::UnsupportedKeyAlgorithm)?,
	};