Use website common names for quick setup wizard

app/src/main/java/eu/faircode/email/ConnectionHelper.java

@@ -37,12 +37,21 @@ import com.sun.mail.iap.ConnectionException;
 import com.sun.mail.util.FolderClosedIOException;
 
 import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.security.cert.Certificate;
+import java.security.cert.CertificateParsingException;
+import java.security.cert.X509Certificate;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
 import java.util.Objects;
 
+import javax.net.SocketFactory;
+import javax.net.ssl.SSLSocket;
+import javax.net.ssl.SSLSocketFactory;
+
 public class ConnectionHelper {
     static final List<String> PREF_NETWORK = Collections.unmodifiableList(Arrays.asList(
             "metered", "roaming", "rlah", "require_validated", "vpn_only" // update network state
@@ -472,4 +481,29 @@ public class ConnectionHelper {
         return Settings.Global.getInt(context.getContentResolver(),
                 Settings.Global.AIRPLANE_MODE_ON, 0) != 0;
     }
+
+    static List<String> getCommonNames(Context context, String domain, int port, int timeout) throws IOException {
+        List<String> result = new ArrayList<>();
+        InetSocketAddress address = new InetSocketAddress(domain, port);
+        SocketFactory factory = SSLSocketFactory.getDefault();
+        try (SSLSocket sslSocket = (SSLSocket) factory.createSocket()) {
+            EntityLog.log(context, "Connecting to " + address);
+            sslSocket.connect(address, timeout);
+            EntityLog.log(context, "Connected " + address);
+
+            sslSocket.setSoTimeout(timeout);
+            sslSocket.startHandshake();
+
+            Certificate[] certs = sslSocket.getSession().getPeerCertificates();
+            for (Certificate cert : certs)
+                if (cert instanceof X509Certificate) {
+                    try {
+                        result.addAll(EntityCertificate.getDnsNames((X509Certificate) cert));
+                    } catch (CertificateParsingException ex) {
+                        Log.w(ex);
+                    }
+                }
+        }
+        return result;
+    }
 }

app/src/main/java/eu/faircode/email/EmailProvider.java

@@ -281,6 +281,34 @@ public class EmailProvider implements Parcelable {
         List<EmailProvider> candidates =
                 new ArrayList<>(_fromDomain(context, domain.toLowerCase(Locale.ROOT), email, discover));
 
+        try {
+            InetAddress iaddr = InetAddress.getByName(domain.toLowerCase(Locale.ROOT));
+            List<String> commonNames =
+                    ConnectionHelper.getCommonNames(context, domain.toLowerCase(Locale.ROOT), 443, SCAN_TIMEOUT);
+            EntityLog.log(context, "Website common names=" + TextUtils.join(",", commonNames));
+            for (String commonName : commonNames) {
+                String altName = commonName;
+                if (altName.startsWith("*.")) {
+                    altName = altName.substring(2);
+                    if (commonNames.contains(altName))
+                        continue;
+                }
+
+                if (!altName.equalsIgnoreCase(domain))
+                    try {
+                        InetAddress ialt = InetAddress.getByName(altName);
+                        if (!ialt.equals(iaddr)) {
+                            EntityLog.log(context, "Using website common name=" + altName);
+                            candidates.addAll(_fromDomain(context, altName.toLowerCase(Locale.ROOT), email, discover));
+                        }
+                    } catch (Throwable ex) {
+                        Log.w(ex);
+                    }
+            }
+        } catch (Throwable ex) {
+            Log.w(ex);
+        }
+
         try {
             DnsHelper.DnsRecord[] records = DnsHelper.lookup(context, domain, "mx");