feat(cryptographic): add certificateFingerprint API method

lib/src/cryptographic.dart

@@ -166,4 +166,22 @@ class Cryptographic {
           ).replaceAll('=', '').substring(0, length);
     return '$prefix$key';
   }
+
+  /// Returns certificate fingerprint.
+  ///
+  /// [asSha256] determines whether returned string looks like sha256 or sha1
+  /// (default is true).
+  ///
+  /// Example:
+  /// ```dart
+  /// Cryptographic().certificateFingerprint(); // "74:67:A0:9C:B6:49:9B:B1:51:74:C2:9F:6C:42:81:52:5C:7A:31:F5:72:75:09:A0:41:08:1F:53:31:E7:D7:41"
+  /// Cryptographic().certificateFingerprint(asSha256: false); // "93:5E:AE:6E:89:6B:CF:C4:76:DD:6D:23:50:10:80:6C:22:9D:55:90"
+  /// ```
+  String certificateFingerprint({bool asSha256 = true}) {
+    final hexString = asSha256 ? tokenHex() : tokenHex(entropy: 20);
+    return [
+      for (var i = 0; i < hexString.length; i += 2)
+        hexString.substring(i, i + 2),
+    ].join(':').toUpperCase();
+  }
 }

test/src/cryptographic_test.dart

@@ -192,5 +192,35 @@ void main() {
         );
       }
     });
+
+    test('returns certificate fingerprint with default params', () {
+      final result = crypto.certificateFingerprint();
+      expect(result.length, equals(95)); // 32 bytes * 2 hex chars + 31 colons
+      expect(":".allMatches(result).length, 31);
+      expect(result.contains(RegExp('[A-Z]')), isTrue);
+      expect(
+        seededCrypto.certificateFingerprint(),
+        equals(seededCrypto.certificateFingerprint()),
+      );
+    });
+
+    test('returns ertificate fingerprint with provided params', () {
+      const params = [
+        // [asSha256, expectedLength, expectedColons]
+        (true, 95, 31), // 32 bytes = 64 hex chars + 31 colons = 95 total
+        (false, 59, 19), // 20 bytes = 40 hex chars + 19 colons = 59 total
+      ];
+
+      for (final (asSha256, expectedLength, expectedColons) in params) {
+        final result = crypto.certificateFingerprint(asSha256: asSha256);
+        expect(result.length, equals(expectedLength));
+        expect(":".allMatches(result).length, expectedColons);
+        expect(result.contains(RegExp('[A-Z]')), isTrue);
+        expect(
+          seededCrypto.certificateFingerprint(asSha256: asSha256),
+          equals(seededCrypto.certificateFingerprint(asSha256: asSha256)),
+        );
+      }
+    });
   });
 }