csr: support populating custom extensions from CSR.

This commit updates the CSR parsing to populate unknown requested
extensions as custom extensions in the built CSR
`CertificateParams.custom_extensions`.

src/csr.rs

@@ -1,5 +1,5 @@
 #[cfg(feature = "x509-parser")]
-use crate::{DistinguishedName, SanType};
+use crate::{CustomExtension, DistinguishedName, SanType};
 #[cfg(feature = "pem")]
 use pem::Pem;
 use std::hash::Hash;
@@ -67,20 +67,48 @@ impl CertificateSigningRequest {
 		params.distinguished_name = DistinguishedName::from_name(&info.subject)?;
 		let raw = info.subject_pki.subject_public_key.data.to_vec();
 
-		if let Some(extensions) = csr.requested_extensions() {
-			for ext in extensions {
-				match ext {
+		// Pull out the extension requests attributes from the CSR.
+		// Note: we avoid using csr.requested_extensions() here because it maps to the parsed
+		// extension value and we want the raw extension value to handle unknown extensions
+		// ourselves.
+		let requested_exts = csr
+			.certification_request_info
+			.iter_attributes()
+			.filter_map(|attr| {
+				if let x509_parser::prelude::ParsedCriAttribute::ExtensionRequest(requested) =
+					&attr.parsed_attribute()
+				{
+					Some(requested.extensions.iter().collect::<Vec<_>>())
+				} else {
+					None
+				}
+			})
+			.flatten()
+			.collect::<Vec<_>>();
+
+		if !requested_exts.is_empty() {
+			for ext in requested_exts {
+				let supported = match ext.parsed_extension() {
 					x509_parser::extensions::ParsedExtension::SubjectAlternativeName(san) => {
 						for name in &san.general_names {
 							params
 								.subject_alt_names
 								.push(SanType::try_from_general(name)?);
 						}
+						true
 					},
 					x509_parser::extensions::ParsedExtension::SubjectKeyIdentifier(ski) => {
 						params.key_identifier = ski.0.to_vec();
+						true
 					},
-					_ => return Err(RcgenError::UnsupportedExtension),
+					_ => false,
+				};
+				if !supported {
+					params.custom_extensions.push(CustomExtension {
+						oid: ext.oid.iter().unwrap().collect(),
+						critical: ext.critical,
+						content: ext.value.to_vec(),
+					})
 				}
 			}
 		}

tests/generic.rs

@@ -335,7 +335,7 @@ mod test_csr_exts {
 mod test_x509_custom_ext {
 	use crate::util;
 
-	use rcgen::{Certificate, CustomExtension};
+	use rcgen::{Certificate, CertificateSigningRequest, CustomExtension};
 	use x509_parser::oid_registry::asn1_rs;
 	use x509_parser::prelude::{
 		FromDer, ParsedCriAttribute, X509Certificate, X509CertificationRequest,
@@ -396,8 +396,20 @@ mod test_x509_custom_ext {
 			.iter()
 			.find(|ext| ext.oid == test_oid)
 			.expect("missing requested custom extension");
-		assert_eq!(custom_ext.critical, true);
+		assert!(custom_ext.critical);
 		assert_eq!(custom_ext.value, test_ext);
+
+		// We should be able to create an rcgen CSR from the serialized CSR.
+		let rcgen_csr = CertificateSigningRequest::from_der(&test_cert_csr_der).unwrap();
+		// The custom extensions should be present in the CSR.
+		let custom_ext = rcgen_csr
+			.params
+			.custom_extensions
+			.iter()
+			.find(|ext| Iterator::eq(ext.oid_components(), test_oid.iter().unwrap()))
+			.expect("missing requested custom extension");
+		assert!(custom_ext.criticality());
+		assert_eq!(custom_ext.content(), test_ext);
 	}
 }