Add SystemPropertyLookup resolver to resolve java system properties (#2064)

Co-authored-by: Joseph Petersen <josephp90@gmail.com>

Author: sboardwell

plugin/src/main/java/io/jenkins/plugins/casc/SecretSourceResolver.java

@@ -46,6 +46,7 @@ public SecretSourceResolver(ConfigurationContext configurationContext) {
         map.put("readFileBase64", FileBase64Lookup.INSTANCE);
         map.put("file", FileStringLookup.INSTANCE);
         map.put("readFile", FileStringLookup.INSTANCE);
+        map.put("sysProp", SystemPropertyLookup.INSTANCE);
         map.put("decodeBase64", DecodeBase64Lookup.INSTANCE);
         map.put("json", JsonLookup.INSTANCE);
         map = Collections.unmodifiableMap(map);
@@ -147,6 +148,21 @@ public String lookup(String key) {
         }
     }
 
+    static class SystemPropertyLookup implements StringLookup {
+
+        static final SystemPropertyLookup INSTANCE = new SystemPropertyLookup();
+
+        @Override
+        public String lookup(@NonNull final String key) {
+            final String output = System.getProperty(key);
+            if (output == null) {
+                LOGGER.log(Level.WARNING, String.format("Configuration import: System Properties did not contain the specified key '%s'. Will default to empty string.", key));
+                return "";
+            }
+            return output;
+        }
+    }
+
     static class FileStringLookup implements StringLookup {
 
         static final FileStringLookup INSTANCE = new FileStringLookup();

plugin/src/test/java/io/jenkins/plugins/casc/SecretSourceResolverTest.java

@@ -3,6 +3,7 @@
 import io.jenkins.plugins.casc.SecretSourceResolver.Base64Lookup;
 import io.jenkins.plugins.casc.SecretSourceResolver.FileBase64Lookup;
 import io.jenkins.plugins.casc.SecretSourceResolver.FileStringLookup;
+import io.jenkins.plugins.casc.SecretSourceResolver.SystemPropertyLookup;
 import java.io.File;
 import java.net.URISyntaxException;
 import java.nio.file.Files;
@@ -46,6 +47,7 @@ public class SecretSourceResolverTest {
     public static final StringLookup DECODE = StringLookupFactory.INSTANCE.base64DecoderStringLookup();
     public static final StringLookup FILE = FileStringLookup.INSTANCE;
     public static final StringLookup BINARYFILE = FileBase64Lookup.INSTANCE;
+    public static final StringLookup SYSPROP = SystemPropertyLookup.INSTANCE;
 
     @Before
     public void initLogging() {
@@ -348,6 +350,24 @@ public void resolve_BinaryFileBase64() throws Exception {
         assertThat(actualBytes, equalTo(expectedBytes));
     }
 
+    @Test
+    public void resolve_SystemProperty() throws Exception {
+        String input = "java.version";
+        String expected = System.getProperty(input);
+        String output = resolve("${sysProp:" + input + "}");
+        assertThat(output, equalTo(SYSPROP.lookup(input)));
+        assertThat(output, equalTo(expected));
+    }
+
+    @Test
+    public void resolve_SystemPropertyNotFound() throws Exception {
+        String input = "java.version.non-existent";
+        String expected = "";
+        String output = resolve("${sysProp:" + input + "}");
+        assertThat(output, equalTo(SYSPROP.lookup(input)));
+        assertThat(output, equalTo(expected));
+    }
+
     @Test
     public void resolve_Json() {
         String input = "{ \"a\": 1, \"b\": 2 }";