feat: Channel binding improvements

scram-client/src/main/java/com/ongres/scram/client/ChannelBindingPolicy.java

@@ -5,6 +5,10 @@
 
 package com.ongres.scram.client;
 
+import java.util.Locale;
+
+import org.jetbrains.annotations.NotNull;
+
 /**
  * Defines the client-side security policies for negotiating channel binding during a SCRAM
  * authentication execution.
@@ -46,9 +50,10 @@ public enum ChannelBindingPolicy {
    * <li>If the server advertises a {@code -PLUS} mechanism and channel binding data is provided,
    * the negotiation upgrades to channel binding and uses the {@code 'p'} GS2 flag.</li>
    * <li>If the server lacks {@code -PLUS} support, the client gracefully downgrades to standard
-   * SCRAM but transmits the {@code 'y'} GS2 flag. This explicitly declares to the server
-   * that the client possesses channel binding capabilities, allowing the server to catch
-   * and terminate malicious downgrade attacks mid-flight.</li>
+   * SCRAM. If channel binding data was provided, the {@code 'y'} GS2 flag is transmitted to
+   * explicitly declare that the client possesses channel binding capabilities, allowing the server
+   * to catch and terminate malicious downgrade attacks mid-flight. If no binding data was
+   * configured, {@code 'n'} is used instead.</li>
    * </ul>
    */
   ALLOW,
@@ -70,5 +75,37 @@ public enum ChannelBindingPolicy {
    * applications requiring strict compliance matching database configurations like PostgreSQL's
    * {@code channel_binding=require}).
    */
-  REQUIRE
+  REQUIRE;
+
+  /**
+   * Returns the {@link ChannelBindingPolicy} constant for the given string value
+   * (case-insensitive).
+   *
+   * <p>Accepted values:
+   * <ul>
+   * <li>{@code "disable"} → {@link #DISABLE}</li>
+   * <li>{@code "allow"} → {@link #ALLOW}</li>
+   * <li>{@code "prefer"} → {@link #ALLOW} (alias for PostgreSQL {@code channel_binding=prefer}
+   * compatibility)</li>
+   * <li>{@code "require"} → {@link #REQUIRE}</li>
+   * </ul>
+   *
+   * @param value the string representation of the policy
+   * @return the matching {@link ChannelBindingPolicy}
+   * @throws IllegalArgumentException if {@code value} does not match any known policy
+   */
+  public static ChannelBindingPolicy of(@NotNull String value) {
+    String lowerValue = value.toLowerCase(Locale.ROOT);
+    switch (lowerValue) {
+      case "disable":
+        return DISABLE;
+      case "allow":
+      case "prefer":
+        return ALLOW;
+      case "require":
+        return REQUIRE;
+      default:
+        throw new IllegalArgumentException("Invalid channel binding value: " + value);
+    }
+  }
 }

scram-client/src/test/java/com/ongres/scram/client/ChannelBindingPolicyTest.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2026 OnGres, Inc.
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+package com.ongres.scram.client;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+class ChannelBindingPolicyTest {
+
+  @ParameterizedTest(name = "''{0}'' -> DISABLE")
+  @ValueSource(strings = {"disable", "DISABLE", "Disable"})
+  void ofDisable(String value) {
+    assertEquals(ChannelBindingPolicy.DISABLE, ChannelBindingPolicy.of(value));
+  }
+
+  @ParameterizedTest(name = "''{0}'' -> ALLOW")
+  @ValueSource(strings = {"allow", "ALLOW", "Allow", "prefer", "PREFER", "Prefer"})
+  void ofAllow(String value) {
+    assertEquals(ChannelBindingPolicy.ALLOW, ChannelBindingPolicy.of(value));
+  }
+
+  @ParameterizedTest(name = "''{0}'' -> REQUIRE")
+  @ValueSource(strings = {"require", "REQUIRE", "Require"})
+  void ofRequire(String value) {
+    assertEquals(ChannelBindingPolicy.REQUIRE, ChannelBindingPolicy.of(value));
+  }
+
+  @Test
+  void ofUnknownValueThrows() {
+    IllegalArgumentException ex = assertThrows(IllegalArgumentException.class,
+        () -> ChannelBindingPolicy.of("unknown"));
+    assertEquals("Invalid channel binding value: unknown", ex.getMessage());
+  }
+}

scram-common/src/main/java/com/ongres/scram/common/util/TlsServerEndpoint.java

@@ -14,10 +14,9 @@
 import java.security.cert.X509Certificate;
 import java.security.spec.PSSParameterSpec;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
 
 import org.jetbrains.annotations.NotNull;
 
@@ -38,10 +37,14 @@ public final class TlsServerEndpoint {
    * A static mapping of universally standard signature OIDs to their underlying digest algorithms.
    * This guarantees resolution even if the JCE provider fails to provide a friendly string name.
    */
-  private static final Map<String, String> OID_TO_DIGEST;
+  private static final Map<String, String> OID_TO_DIGEST = digestAlgorithmByOid();
 
-  static {
-    ConcurrentMap<String, String> map = new ConcurrentHashMap<>();
+  private TlsServerEndpoint() {
+    throw new IllegalStateException("Utility class");
+  }
+
+  private static Map<String, String> digestAlgorithmByOid() {
+    Map<String, String> map = new HashMap<>(64);
     // OIDs associated with RSA Signatures
     map.put("1.2.840.113549.1.1.4", "MD5"); // MD5withRSA
     map.put("1.2.840.113549.1.1.5", "SHA-1"); // SHA1withRSA
@@ -75,12 +78,7 @@ public final class TlsServerEndpoint {
     map.put("2.16.840.1.101.3.4.3.6", "SHA3-256"); // SHA3-256withDSA
     map.put("2.16.840.1.101.3.4.3.7", "SHA3-384"); // SHA3-384withDSA
     map.put("2.16.840.1.101.3.4.3.8", "SHA3-512"); // SHA3-512withDSA
-
-    OID_TO_DIGEST = Collections.unmodifiableMap(map);
-  }
-
-  private TlsServerEndpoint() {
-    throw new IllegalStateException("Utility class");
+    return Collections.unmodifiableMap(map);
   }
 
   /**
@@ -146,16 +144,18 @@ private static MessageDigest getDigestAlgorithm(final X509Certificate serverCert
 
     // Normalize the hash name (Applies to both Traditional and RSASSA-PSS)
     switch (algorithmName) {
-      // Enforce RFC 5929 Mandatory Upgrades to SHA-256
       case "MD5":
       case "SHA1":
       case "SHA-1":
-      case "SHA256":
+        // Enforce RFC 5929 Mandatory Upgrades to SHA-256
         algorithmName = "SHA-256";
         break;
       case "SHA224":
         algorithmName = "SHA-224";
         break;
+      case "SHA256":
+        algorithmName = "SHA-256";
+        break;
       case "SHA384":
         algorithmName = "SHA-384";
         break;
@@ -177,28 +177,6 @@ private static MessageDigest getDigestAlgorithm(final X509Certificate serverCert
     return MessageDigest.getInstance(algorithmName);
   }
 
-  /**
-   * The hash of the TLS server's certificate [RFC5280] as it appears, octet for octet, in the
-   * server's Certificate message.
-   *
-   * @param serverCert the TLS server's peer certificate
-   * @return the hash of the TLS server's peer certificate
-   * @throws CertificateEncodingException if an encoding error occurs.
-   * @deprecated this method silently swallows {@link NoSuchAlgorithmException} and returns an
-   *             empty array. It is replaced by {@link #getChannelBindingHash(X509Certificate)}
-   *             and will be removed in a future release.
-   */
-  @Deprecated
-  public static byte @NotNull [] getChannelBindingData(final @NotNull X509Certificate serverCert)
-      throws CertificateEncodingException {
-    try {
-      return getChannelBindingHash(serverCert);
-    } catch (NoSuchAlgorithmException e) {
-      // Preserve the old (and dangerous) silent-failure behavior for backward compatibility
-      return new byte[0];
-    }
-  }
-
   /**
    * Computes the hash of the TLS server's certificate [RFC5280] as it appears, octet for octet, in
    * the server's Certificate message, for use as {@code "tls-server-end-point"} channel binding.

scram-common/src/test/java/com/ongres/scram/common/util/TlsServerEndpointTest.java

@@ -54,9 +54,13 @@ private static Stream<Arguments> provideValidCertificates() {
         Arguments.of(loadCertificate("/SHA3-512withECDSA.pem"),
             "SHA3-512withECDSA", "SHA3-512"),
 
-        // Parameterized RSASSA-PSS (The generated PEM uses SHA-384)
+        // Parameterized RSASSA-PSS with SHA-384 digest
         Arguments.of(loadCertificate("/RSASSA-PSS.pem"),
-            "RSASSA-PSS", "SHA-384"));
+            "RSASSA-PSS", "SHA-384"),
+
+        // RSASSA-PSS with SHA-1 digest: RFC 5929 mandatory upgrade SHA-1 -> SHA-256
+        Arguments.of(loadCertificate("/RSASSA-PSS-SHA1.pem"),
+            "RSASSA-PSS", "SHA-256"));
   }
 
   /**
@@ -68,7 +72,6 @@ private static Stream<Arguments> provideUnsupportedCertificates() {
         Arguments.of(loadCertificate("/Ed448.pem"), "Ed448"));
   }
 
-  @SuppressWarnings("deprecation")
   @ParameterizedTest(name = "Extracts correct binding hash for {1} -> expects {2}")
   @MethodSource("provideValidCertificates")
   void testValidCertificateChannelBinding(X509Certificate cert, String sigAlg,
@@ -87,34 +90,23 @@ void testValidCertificateChannelBinding(X509Certificate cert, String sigAlg,
     byte[] actualHash = assertDoesNotThrow(() -> TlsServerEndpoint.getChannelBindingHash(cert));
     assertArrayEquals(expectedHash, actualHash,
         "getChannelBindingHash did not return the expected digest bytes");
-
-    // 4. Test the deprecated method
-    byte[] actualDeprecatedData = assertDoesNotThrow(() -> TlsServerEndpoint.getChannelBindingData(cert));
-    assertArrayEquals(expectedHash, actualDeprecatedData,
-        "Deprecated getChannelBindingData did not match expected digest bytes");
   }
 
-  @SuppressWarnings({ "deprecation" })
   @ParameterizedTest(name = "Rejects unsupported/pure algorithm {1} (Postgres parity)")
   @MethodSource("provideUnsupportedCertificates")
   void testUnsupportedCertificatesFail(X509Certificate cert, String sigAlg) {
     // Ensure the generated PEM matches the test expectation
     assertEquals(sigAlg, cert.getSigAlgName(),
         "Loaded certificate does not match expected algorithm");
 
-    // 1. Ensure the modern method throws an exception
+    // Ensure the modern method throws an exception
     NoSuchAlgorithmException exception = assertThrows(NoSuchAlgorithmException.class,
         () -> TlsServerEndpoint.getChannelBindingHash(cert));
 
     assertEquals(String.format(Locale.ROOT,
         "Could not determine server certificate signature algorithm. Name: %s, OID: %s",
         cert.getSigAlgName(), cert.getSigAlgOID()),
         exception.getMessage());
-
-    // 2. Ensure the deprecated method swallows the exception and returns an empty array
-    byte[] deprecatedResult = assertDoesNotThrow(() -> TlsServerEndpoint.getChannelBindingData(cert));
-    assertArrayEquals(new byte[0], deprecatedResult,
-        "Deprecated method must return byte[0] on unsupported algorithms");
   }
 
   /**

scram-common/src/test/resources/RSASSA-PSS-SHA1.pem

@@ -0,0 +1,19 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----