Auto merge of #26716 - jdm:selfsigned, r=Manishearth,asajeffrey

Add UI for bypassing SSL handshake failures

There are several parts to these changes:
1. resurrecting the network error classification code to distinguish between SSL failures and other network errors
1. adding an SSL verification callback to support verifying certs against a list that can change at runtime, rather than just at program initialization
1. exposing a privileged chrome://allowcert URI which accepts the PEM cert contents along with a secret token
1. extracting the PEM cert contents out of the network layer when a handshake failure occurs, and getting them into the HTML that is parsed when an SSL failure occurs
1. adding a button in the handshake failure page that performs an XHR to chrome://allowcert with knowledge of the secret token and the PEM cert contents, before reloading the original URL that failed

The presence of the secret token means that while the chrome://allowcert URL is currently visible to web content, they cannot make use of it to inject arbitrary certs into the verification process.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #26683
- [x] These changes do not require tests because the UI requires user activation and can't clearly be automated

components/script/dom/servoparser/mod.rs

@@ -731,9 +731,9 @@ impl FetchResponseListener for ParserContext {
                 FetchMetadata::Unfiltered(m) => m,
                 FetchMetadata::Filtered { unsafe_, .. } => unsafe_,
             }),
-            Err(NetworkError::SslValidation(url, reason)) => {
-                ssl_error = Some(reason);
-                let mut meta = Metadata::default(url);
+            Err(NetworkError::SslValidation(reason, cert_bytes)) => {
+                ssl_error = Some((reason, cert_bytes));
+                let mut meta = Metadata::default(self.url.clone());
                 let mime: Option<Mime> = "text/html".parse().ok();
                 meta.set_content_type(mime.as_ref());
                 Some(meta)
@@ -815,10 +815,14 @@ impl FetchResponseListener for ParserContext {
             },
             Some(ref mime) if mime.type_() == mime::TEXT && mime.subtype() == mime::HTML => {
                 // Handle text/html
-                if let Some(reason) = ssl_error {
+                if let Some((reason, bytes)) = ssl_error {
                     self.is_synthesized_document = true;
                     let page = resources::read_string(Resource::BadCertHTML);
                     let page = page.replace("${reason}", &reason);
+                    let page =
+                        page.replace("${bytes}", std::str::from_utf8(&bytes).unwrap_or_default());
+                    let page =
+                        page.replace("${secret}", &net_traits::PRIVILEGED_SECRET.to_string());
                     parser.push_string_input_chunk(page);
                     parser.parse_sync();
                 }