Deprecate crypto.codec.Base64

In commit 85719fc Base64 was removed. However, this class was never
deprecated properly. This commit adds it back and marks it as deprecated.

Fixes gh-4421

crypto/src/test/java/org/springframework/security/crypto/codec/Base64Tests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2002-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.security.crypto.codec;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.*;
+
+/**
+ * @author Luke Taylor
+ */
+public class Base64Tests {
+
+	@Test
+	public void isBase64ReturnsTrueForValidBase64() {
+		new Base64(); // unused
+
+		assertThat(Base64.isBase64(new byte[] { (byte) 'A', (byte) 'B', (byte) 'C',
+				(byte) 'D' })).isTrue();
+	}
+
+	@Test
+	public void isBase64ReturnsFalseForInvalidBase64() throws Exception {
+		// Include invalid '`' character
+		assertThat(Base64.isBase64(new byte[] { (byte) 'A', (byte) 'B', (byte) 'C',
+				(byte) '`' })).isFalse();
+	}
+
+	@Test(expected = NullPointerException.class)
+	public void isBase64RejectsNull() {
+		Base64.isBase64(null);
+	}
+
+	@Test(expected = IllegalArgumentException.class)
+	public void isBase64RejectsInvalidLength() {
+		Base64.isBase64(new byte[] { (byte) 'A' });
+	}
+}