tests: add BetterTLS path building test suite.

[`git cherry-pick 4a39e2b`, with support
for Edition 2018 added by Brian.]

This commit introduces the Netflix BetterTLS[0]'s path building test
suite to the webpki integration tests.

This project has a test runner for Rustls that will stand up TLS servers
to exercise these tests but:

* It requires Go.
* It needs Rustls in order to do a full TLS handshake with the test
  servers.
* It's slower than testing the path building directly without the TLS
  bits.

To avoid these issues this commit takes a different approach and vendors
the exported path building test suite. This is a supported feature[1] of
the upstream project and allow us to directly test webpki's path
building against the test suite without needing Rustls or Go.

[0]: https://github.com/Netflix/bettertls
[1]: https://github.com/Netflix/bettertls#exporting-tests-to-run-outside-of-the-bettertls-executor

Cargo.toml

@@ -76,6 +76,8 @@ untrusted = "0.7.1"
 [dev-dependencies]
 base64 = "0.9.1"
 rcgen = { version = "=0.11.1", default-features = false }
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
 
 [profile.bench]
 opt-level = 3

tests/better_tls.rs

@@ -0,0 +1,95 @@
+use serde::Deserialize;
+use std::{collections::HashMap, convert::TryFrom};
+use webpki::TrustAnchor;
+
+#[test]
+pub fn path_building() {
+    let raw_json = include_bytes!("../third-party/bettertls/pathbuilding.tests.json");
+    let better_tls: BetterTls = serde_json::from_slice(raw_json).expect("invalid test JSON");
+    println!("Testing BetterTLS revision {:?}", better_tls.revision);
+
+    let root_der = &better_tls.root_der();
+    let roots = &[TrustAnchor::try_from_cert_der(root_der).expect("invalid trust anchor")];
+    let trust_anchors = &webpki::TlsServerTrustAnchors(roots);
+
+    let path_building_suite = better_tls
+        .suites
+        .get("pathbuilding")
+        .expect("missing pathbuilding suite");
+
+    for testcase in &path_building_suite.test_cases {
+        println!("Testing path building test case {:?}", testcase.id);
+
+        let certs_der = testcase.certs_der();
+        let ee_der = &certs_der[0];
+        let intermediates = &certs_der[1..]
+            .iter()
+            .map(|cert| cert.as_slice())
+            .collect::<Vec<_>>();
+
+        let ee_cert =
+            webpki::EndEntityCert::try_from(ee_der.as_slice()).expect("invalid end entity cert");
+
+        // Set the time to the time of test case generation. This ensures that the test case
+        // certificates won't expire.
+        let now = webpki::Time::from_seconds_since_unix_epoch(1_688_651_734);
+
+        let result = ee_cert.verify_is_valid_tls_server_cert(
+            &[&webpki::ECDSA_P256_SHA256], // All of the BetterTLS testcases use P256 keys.
+            trust_anchors,
+            intermediates,
+            now,
+        );
+
+        match testcase.expected {
+            ExpectedResult::Accept => assert!(result.is_ok(), "expected success, got {:?}", result),
+            ExpectedResult::Reject => {
+                assert!(result.is_err(), "expected failure, got {:?}", result)
+            }
+        }
+    }
+}
+
+#[derive(Deserialize, Debug)]
+struct BetterTls {
+    #[serde(rename(deserialize = "betterTlsRevision"))]
+    revision: String,
+    #[serde(rename(deserialize = "trustRoot"))]
+    root: String,
+    suites: HashMap<String, BetterTlsSuite>,
+}
+
+impl BetterTls {
+    fn root_der(&self) -> Vec<u8> {
+        base64::decode(&self.root).expect("invalid trust anchor base64")
+    }
+}
+
+#[derive(Deserialize, Debug)]
+struct BetterTlsSuite {
+    #[serde(rename(deserialize = "testCases"))]
+    test_cases: Vec<BetterTlsTest>,
+}
+
+#[derive(Deserialize, Debug)]
+struct BetterTlsTest {
+    id: u32,
+    certificates: Vec<String>,
+    expected: ExpectedResult,
+}
+
+impl BetterTlsTest {
+    fn certs_der(&self) -> Vec<Vec<u8>> {
+        self.certificates
+            .iter()
+            .map(|cert| base64::decode(cert).expect("invalid cert base64"))
+            .collect()
+    }
+}
+
+#[derive(Deserialize, Debug)]
+#[serde(rename_all = "UPPERCASE")]
+enum ExpectedResult {
+    Accept,
+    Reject,
+}

third-party/bettertls/LICENSE

@@ -0,0 +1,177 @@
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