Revert "fix: disambiguate DER decoders for RSA keys"

This reverts commit ab88daa.

Author: thieman

src/signer/rsa.rs

@@ -3,9 +3,9 @@
 // This product includes software developed at Datadog (https://www.datadoghq.com/)
 // Copyright 2026 Datadog, Inc.
 
-use pkcs1::der::Decode as Pkcs1Decode;
+use pkcs1::der::Decode as _;
 use pkcs1::RsaPrivateKey;
-use pkcs8::der::Decode as Pkcs8Decode;
+use pkcs8::der::Decode as _;
 use pkcs8::PrivateKeyInfoRef;
 use rustls::pki_types::PrivateKeyDer;
 use rustls::{Error, SignatureAlgorithm, SignatureScheme};
@@ -54,15 +54,17 @@ impl RsaSigningKey {
     pub(super) fn new(der: &PrivateKeyDer<'_>) -> Result<Self, Error> {
         let key = match der {
             PrivateKeyDer::Pkcs1(private_pkcs1_key_der) => {
-                Pkcs1Decode::from_der(private_pkcs1_key_der.secret_pkcs1_der())
+                RsaPrivateKey::from_der(private_pkcs1_key_der.secret_pkcs1_der())
                     .map_err(|e| Error::General(format!("Failed to parse PKCS1 key: {e}")))
             }
             PrivateKeyDer::Pkcs8(private_pkcs8_key_der) => {
-                let pki: PrivateKeyInfoRef =
-                    Pkcs8Decode::from_der(private_pkcs8_key_der.secret_pkcs8_der())
-                        .map_err(|e| Error::General(format!("Failed to parse PKCS8 key: {e}")))?;
-                Pkcs1Decode::from_der(pki.private_key.as_bytes())
-                    .map_err(|e| Error::General(format!("Failed to parse PKCS8 RSA key: {e}")))
+                PrivateKeyInfoRef::from_der(private_pkcs8_key_der.secret_pkcs8_der())
+                    .map_err(|e| Error::General(format!("Failed to parse PKCS8 key: {e}")))
+                    .and_then(|pki| {
+                        RsaPrivateKey::from_der(pki.private_key.as_bytes()).map_err(|e| {
+                            Error::General(format!("Failed to parse PKCS8 RSA key: {e}"))
+                        })
+                    })
             }
             _ => Err(Error::General("Unsupported key format".to_string())),
         }?;