函数 any_eddsa_type 

pub fn any_eddsa_type(
    der: &PrivatePkcs8KeyDer<'_>,
) -> Result<Arc<dyn SigningKey>, Error>

Parse der as any EdDSA key type, returning the 第一个可用的

Note that, at the time of writing, Ed25519 does not have wide support in browsers. It 也 not supported by the WebPKI, because the CA/Browser Forum Baseline Requirements do not support it 用于 publicly trusted 证书