Take cert_der by reference in fetch_ohttp_keys_with_cert

The cert_der parameter is only passed to
Certificate::from_der which borrows it, so accept &[u8]
instead of Vec<u8>. Fix call sites in payjoin-cli and
payjoin-test-utils accordingly.

Other pub fns in io.rs and ohttp.rs keep ownership where
consumed (ohttp_context, impl IntoUrl).

Author: DanGould

payjoin-cli/src/app/v2/ohttp.rs

@@ -85,7 +85,7 @@ async fn fetch_ohttp_keys(
                     payjoin::io::fetch_ohttp_keys_with_cert(
                         selected_relay.as_str(),
                         payjoin_directory.as_str(),
-                        cert_der,
+                        &cert_der,
                     )
                     .await
                 } else {

payjoin-test-utils/src/lib.rs

@@ -103,7 +103,7 @@ impl TestServices {
         fetch_ohttp_keys_with_cert(
             self.ohttp_relay_url().as_str(),
             self.directory_url().as_str(),
-            self.cert(),
+            &self.cert(),
         )
         .await
     }

payjoin/src/core/io.rs

@@ -45,13 +45,13 @@ pub async fn fetch_ohttp_keys(
 pub async fn fetch_ohttp_keys_with_cert(
     ohttp_relay: impl IntoUrl,
     payjoin_directory: impl IntoUrl,
-    cert_der: Vec<u8>,
+    cert_der: &[u8],
 ) -> Result<OhttpKeys, Error> {
     let ohttp_keys_url = payjoin_directory.into_url()?.join("/.well-known/ohttp-gateway")?;
     let proxy = Proxy::all(ohttp_relay.into_url()?.as_str())?;
     let client = Client::builder()
         .use_rustls_tls()
-        .add_root_certificate(reqwest::tls::Certificate::from_der(&cert_der)?)
+        .add_root_certificate(reqwest::tls::Certificate::from_der(cert_der)?)
         .proxy(proxy)
         .http1_only()
         .build()?;