Add SSL certificate checker and tests

public/app.js

@@ -199,3 +199,167 @@ dnsForm.addEventListener("submit", async (event) => {
     dnsButton.textContent = "Look Up DNS";
   }
 });
+// ---------------------------------------------------------
+// SSL Certificate Checker
+// ---------------------------------------------------------
+
+// Get references to the SSL form and result elements.
+const sslForm = document.getElementById("ssl-form");
+const sslHostnameInput = document.getElementById(
+  "ssl-hostname-input"
+);
+const sslButton = document.getElementById("ssl-button");
+const sslMessage = document.getElementById("ssl-message");
+const sslResultPanel = document.getElementById(
+  "ssl-result-panel"
+);
+
+const sslStatusBadge = document.getElementById(
+  "ssl-status-badge"
+);
+const sslHostname = document.getElementById("ssl-hostname");
+const sslDaysRemaining = document.getElementById(
+  "ssl-days-remaining"
+);
+const sslValidFrom = document.getElementById("ssl-valid-from");
+const sslValidTo = document.getElementById("ssl-valid-to");
+const sslProtocol = document.getElementById("ssl-protocol");
+const sslCipher = document.getElementById("ssl-cipher");
+const sslAddress = document.getElementById("ssl-address");
+const sslCheckedAt = document.getElementById("ssl-checked-at");
+
+const sslSubject = document.getElementById("ssl-subject");
+const sslIssuer = document.getElementById("ssl-issuer");
+const sslFingerprint = document.getElementById(
+  "ssl-fingerprint"
+);
+
+const sslAuthorizationErrorBlock = document.getElementById(
+  "ssl-authorization-error-block"
+);
+const sslAuthorizationError = document.getElementById(
+  "ssl-authorization-error"
+);
+
+// Convert certificate date strings into a readable local date.
+function formatCertificateDate(value) {
+  if (!value) {
+    return "Unknown";
+  }
+
+  const date = new Date(value);
+
+  if (Number.isNaN(date.getTime())) {
+    return value;
+  }
+
+  return date.toLocaleString();
+}
+
+// Choose readable text for the certificate expiration state.
+function getExpirationText(daysRemaining) {
+  if (daysRemaining === null || daysRemaining === undefined) {
+    return "Unknown";
+  }
+
+  if (daysRemaining < 0) {
+    return `${Math.abs(daysRemaining)} days expired`;
+  }
+
+  if (daysRemaining === 0) {
+    return "Expires today";
+  }
+
+  return `${daysRemaining} days`;
+}
+
+// Handle SSL certificate form submissions.
+sslForm.addEventListener("submit", async (event) => {
+  event.preventDefault();
+
+  const hostname = sslHostnameInput.value.trim();
+
+  // Reset the SSL interface before beginning the request.
+  sslMessage.textContent = "Checking certificate...";
+  sslMessage.className = "status-message";
+  sslResultPanel.hidden = true;
+  sslButton.disabled = true;
+  sslButton.textContent = "Checking...";
+
+  try {
+    const response = await fetch("/api/ssl", {
+      method: "POST",
+      headers: {
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({ hostname }),
+    });
+
+    const result = await response.json();
+
+    if (!response.ok) {
+      throw new Error(
+        result.error || "The SSL certificate check failed."
+      );
+    }
+
+    // Show whether Node trusted the certificate chain and hostname.
+    if (result.authorized) {
+      sslStatusBadge.textContent = "Valid";
+      sslStatusBadge.className = "status-badge online";
+    } else {
+      sslStatusBadge.textContent = "Not trusted";
+      sslStatusBadge.className = "status-badge offline";
+    }
+
+    // Populate the certificate summary.
+    sslHostname.textContent = result.hostname;
+    sslDaysRemaining.textContent = getExpirationText(
+      result.daysRemaining
+    );
+
+    sslValidFrom.textContent = formatCertificateDate(
+      result.validFrom
+    );
+    sslValidTo.textContent = formatCertificateDate(
+      result.validTo
+    );
+
+    sslProtocol.textContent = result.protocol || "Unknown";
+    sslCipher.textContent = result.cipher || "Unknown";
+
+    sslAddress.textContent = result.resolvedAddress
+      ? `${result.resolvedAddress} (IPv${result.addressFamily})`
+      : "Unknown";
+
+    sslCheckedAt.textContent = formatCertificateDate(
+      result.checkedAt
+    );
+
+    // Populate the longer certificate values.
+    sslSubject.textContent = result.subject || "Unknown";
+    sslIssuer.textContent = result.issuer || "Unknown";
+    sslFingerprint.textContent =
+      result.fingerprint256 || "Unavailable";
+
+    // Show the authorization problem only when one exists.
+    if (result.authorizationError) {
+      sslAuthorizationError.textContent =
+        result.authorizationError;
+      sslAuthorizationErrorBlock.hidden = false;
+    } else {
+      sslAuthorizationError.textContent = "";
+      sslAuthorizationErrorBlock.hidden = true;
+    }
+
+    sslMessage.textContent =
+      "Certificate check completed.";
+    sslResultPanel.hidden = false;
+  } catch (error) {
+    sslMessage.textContent = error.message;
+    sslMessage.className = "status-message error";
+  } finally {
+    sslButton.disabled = false;
+    sslButton.textContent = "Check Certificate";
+  }
+});