Improve SAML tests resiliency to auto-formatting (#48517)

Backport of #48452.

The SAML tests have large XML documents within which various parameters
are replaced. At present, if these test are auto-formatted, the XML
documents get strung out over many, many lines, and are basically
illegible.

Fix this by using named placeholders for variables, and indent the
multiline XML documents.

The tests in `SamlSpMetadataBuilderTests` deserve a special mention,
because they include a number of certificates in Base64. I extracted
these into variables, for additional legibility.

Author: pugnascotia

test/framework/src/main/java/org/elasticsearch/common/util/NamedFormatter.java

@@ -0,0 +1,87 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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.elasticsearch.common.util;
+
+import java.util.Map;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * A formatter that allows named placeholders e.g. "%(param)" to be replaced.
+ */
+public class NamedFormatter {
+    private static final Pattern PARAM_REGEX = Pattern
+        .compile(
+            // Match either any backlash-escaped characters, or a "%(param)" pattern.
+            // COMMENTS is specified to allow whitespace in this pattern, for clarity
+            "\\\\(.) | (% \\( ([^)]+) \\) )",
+            Pattern.COMMENTS
+        );
+
+    private NamedFormatter() {}
+
+    /**
+     * Replaces named parameters of the form <code>%(param)</code> in format strings. For example:
+     *
+     * <ul>
+     * <li><code>NamedFormatter.format("Hello, %(name)!", Map.of("name", "world"))</code> → <code>"Hello, world!"</code></li>
+     * <li><code>NamedFormatter.format("Hello, \%(name)!", Map.of("name", "world"))</code> → <code>"Hello, %(world)!"</code></li>
+     * <li><code>NamedFormatter.format("Hello, %(oops)!", Map.of("name", "world"))</code> → {@link IllegalArgumentException}</li>
+     * </ul>
+     *
+     * @param fmt The format string. Any <code>%(param)</code> is replaced by its corresponding value in the <code>values</code> map.
+     *             Parameter patterns can be escaped by prefixing with a backslash.
+     * @param values a map of parameter names to values.
+     * @return The formatted string.
+     * @throws IllegalArgumentException if a parameter is found in the format string with no corresponding value
+     */
+    public static String format(String fmt, Map<String, Object> values) {
+        final Matcher matcher = PARAM_REGEX.matcher(fmt);
+
+        boolean result = matcher.find();
+
+        if (result) {
+            final StringBuffer sb = new StringBuffer();
+            do {
+                String replacement;
+
+                // Escaped characters are unchanged
+                if (matcher.group(1) != null) {
+                    replacement = matcher.group(1);
+                } else {
+                    final String paramName = matcher.group(3);
+                    if (values.containsKey(paramName) == true) {
+                        replacement = values.get(paramName).toString();
+                    } else {
+                        throw new IllegalArgumentException("No parameter value for %(" + paramName + ")");
+                    }
+                }
+
+                matcher.appendReplacement(sb, replacement);
+                result = matcher.find();
+            } while (result);
+
+            matcher.appendTail(sb);
+            return sb.toString();
+        }
+
+        return fmt;
+    }
+}

test/framework/src/test/java/org/elasticsearch/common/util/NamedFormatterTests.java

@@ -0,0 +1,64 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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.elasticsearch.common.util;
+
+import org.elasticsearch.test.ESTestCase;
+import org.junit.Rule;
+import org.junit.rules.ExpectedException;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static java.util.Collections.singletonMap;
+import static org.hamcrest.Matchers.equalTo;
+
+public class NamedFormatterTests extends ESTestCase {
+    @Rule
+    public ExpectedException thrown = ExpectedException.none();
+
+    public void testPatternAreFormatted() {
+        assertThat(NamedFormatter.format("Hello, %(name)!", singletonMap("name", "world")), equalTo("Hello, world!"));
+    }
+
+    public void testDuplicatePatternsAreFormatted() {
+        assertThat(NamedFormatter.format("Hello, %(name) and %(name)!", singletonMap("name", "world")), equalTo("Hello, world and world!"));
+    }
+
+    public void testMultiplePatternsAreFormatted() {
+        final Map<String, Object> values = new HashMap<>();
+        values.put("name", "world");
+        values.put("second_name", "fred");
+
+        assertThat(
+            NamedFormatter.format("Hello, %(name) and %(second_name)!", values),
+            equalTo("Hello, world and fred!")
+        );
+    }
+
+    public void testEscapedPatternsAreNotFormatted() {
+        assertThat(NamedFormatter.format("Hello, \\%(name)!", singletonMap("name", "world")), equalTo("Hello, %(name)!"));
+    }
+
+    public void testUnknownPatternsThrowException() {
+        thrown.expect(IllegalArgumentException.class);
+        thrown.expectMessage("No parameter value for %(name)");
+        NamedFormatter.format("Hello, %(name)!", singletonMap("foo", "world"));
+    }
+}