Add X509StoreContextRef::init_without_cleanup

As X509_STORE_CTX_init requires its arguments to outlive
the store context, we take ownership of all of them
and put them in the store context's ex data, ensuring
the soundness of the operation without the mandatory
call to X509_STORE_CTX_cleanup after a closure
is run.

boring/src/x509/mod.rs

@@ -21,6 +21,7 @@ use std::path::Path;
 use std::ptr;
 use std::slice;
 use std::str;
+use std::sync::{LazyLock, Once};
 
 use crate::asn1::{
     Asn1BitStringRef, Asn1IntegerRef, Asn1Object, Asn1ObjectRef, Asn1StringRef, Asn1TimeRef,
@@ -48,6 +49,15 @@ pub mod verify;
 #[cfg(test)]
 mod tests;
 
+static STORE_INDEX: LazyLock<Index<X509StoreContext, store::X509Store>> =
+    LazyLock::new(|| X509StoreContext::new_ex_index().unwrap());
+
+static CERT_INDEX: LazyLock<Index<X509StoreContext, X509>> =
+    LazyLock::new(|| X509StoreContext::new_ex_index().unwrap());
+
+static CERT_CHAIN_INDEX: LazyLock<Index<X509StoreContext, Stack<X509>>> =
+    LazyLock::new(|| X509StoreContext::new_ex_index().unwrap());
+
 foreign_type_and_impl_send_sync! {
     type CType = ffi::X509_STORE_CTX;
     fn drop = ffi::X509_STORE_CTX_free;
@@ -197,6 +207,38 @@ impl X509StoreContextRef {
         }
     }
 
+    pub fn init_without_cleanup(
+        &mut self,
+        trust: store::X509Store,
+        cert: X509,
+        cert_chain: Stack<X509>,
+    ) -> Result<(), ErrorStack> {
+        unsafe {
+            if let Err(e) = cvt(ffi::X509_STORE_CTX_init(
+                self.as_ptr(),
+                trust.as_ptr(),
+                cert.as_ptr(),
+                cert_chain.as_ptr(),
+            )) {
+                ffi::X509_STORE_CTX_cleanup(self.as_ptr());
+
+                return Err(e);
+            }
+        }
+
+        self.set_ex_data(*STORE_INDEX, trust);
+        self.set_ex_data(*CERT_INDEX, cert);
+        self.set_ex_data(*CERT_CHAIN_INDEX, cert_chain);
+
+        Ok(())
+    }
+
+    /// Returns a reference to the X509 verification configuration.
+    #[corresponds(X509_STORE_CTX_get0_param)]
+    pub fn verify_param(&mut self) -> &X509VerifyParamRef {
+        unsafe { X509VerifyParamRef::from_ptr(ffi::X509_STORE_CTX_get0_param(self.as_ptr())) }
+    }
+
     /// Returns a mutable reference to the X509 verification configuration.
     #[corresponds(X509_STORE_CTX_get0_param)]
     pub fn verify_param_mut(&mut self) -> &mut X509VerifyParamRef {