Fixes #268. Added interceptor to Relocate configuration properties.

implementation/src/main/java/io/smallrye/config/FallbackConfigSourceInterceptor.java

@@ -0,0 +1,31 @@
+package io.smallrye.config;
+
+import java.util.Map;
+import java.util.function.Function;
+
+import javax.annotation.Priority;
+
+@Priority(500)
+public class FallbackConfigSourceInterceptor implements ConfigSourceInterceptor {
+    private final Function<String, String> mapping;
+
+    public FallbackConfigSourceInterceptor(final Function<String, String> mapping) {
+        this.mapping = mapping != null ? mapping : Function.identity();
+    }
+
+    public FallbackConfigSourceInterceptor(final Map<String, String> mappings) {
+        this(name -> mappings.getOrDefault(name, name));
+    }
+
+    @Override
+    public ConfigValue getValue(final ConfigSourceInterceptorContext context, final String name) {
+        ConfigValue configValue = context.proceed(name);
+        if (configValue == null) {
+            final String map = mapping.apply(name);
+            if (!name.equals(map)) {
+                configValue = context.proceed(map);
+            }
+        }
+        return configValue;
+    }
+}

implementation/src/main/java/io/smallrye/config/RelocateConfigSourceInterceptor.java

@@ -1,18 +1,29 @@
 package io.smallrye.config;
 
+import java.util.Map;
+import java.util.function.Function;
+
 import javax.annotation.Priority;
 
-@Priority(200)
+@Priority(300)
 public class RelocateConfigSourceInterceptor implements ConfigSourceInterceptor {
-    private static final String RELOCATE_PREFIX = "%relocate.";
+    private final Function<String, String> mapping;
+
+    public RelocateConfigSourceInterceptor(final Function<String, String> mapping) {
+        this.mapping = mapping != null ? mapping : Function.identity();
+    }
+
+    public RelocateConfigSourceInterceptor(final Map<String, String> mappings) {
+        this(name -> mappings.getOrDefault(name, name));
+    }
 
     @Override
     public ConfigValue getValue(final ConfigSourceInterceptorContext context, final String name) {
-        final ConfigValue configValue = context.proceed(name);
-        if (configValue != null && configValue.getValue().startsWith(RELOCATE_PREFIX)) {
-            return context.proceed(configValue.getValue().substring(RELOCATE_PREFIX.length()));
+        final String map = mapping.apply(name);
+        ConfigValue configValue = context.proceed(map);
+        if (configValue == null && !name.equals(map)) {
+            configValue = context.proceed(name);
         }
-
         return configValue;
     }
 }

implementation/src/test/java/io/smallrye/config/MappingConfigSourceInterceptorTest.java

@@ -0,0 +1,58 @@
+package io.smallrye.config;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.HashMap;
+
+import org.eclipse.microprofile.config.Config;
+import org.junit.Test;
+
+public class MappingConfigSourceInterceptorTest {
+    @Test
+    public void relocateAndFallback() {
+        final Config config = buildConfig("mp.jwt.token.header", "Authorization",
+                "mp.jwt.token.cookie", "Bearer");
+
+        assertEquals("Authorization", config.getValue("smallrye.jwt.token.header", String.class));
+        assertEquals("Bearer", config.getValue("smallrye.jwt.token.cookie", String.class));
+    }
+
+    @Test
+    public void relocate() {
+        final Config config = buildConfig(
+                "smallrye.jwt.token.header", "Cookie",
+                "mp.jwt.token.header", "Authorization");
+
+        assertEquals("Authorization", config.getValue("smallrye.jwt.token.header", String.class));
+    }
+
+    @Test
+    public void fallback() {
+        final Config config = buildConfig(
+                "smallrye.jwt.token.cookie", "jwt",
+                "mp.jwt.token.cookie", "Bearer");
+
+        assertEquals("jwt", config.getValue("smallrye.jwt.token.cookie", String.class));
+    }
+
+    private static Config buildConfig(String... keyValues) {
+        return new SmallRyeConfigBuilder()
+                .addDefaultSources()
+                .withSources(KeyValuesConfigSource.config(keyValues))
+                .withInterceptors(
+                        new RelocateConfigSourceInterceptor(
+                                new HashMap<String, String>() {
+                                    {
+                                        put("smallrye.jwt.token.header", "mp.jwt.token.header");
+                                    }
+                                }),
+                        new FallbackConfigSourceInterceptor(
+                                new HashMap<String, String>() {
+                                    {
+                                        put("smallrye.jwt.token.header", "mp.jwt.token.header");
+                                        put("smallrye.jwt.token.cookie", "mp.jwt.token.cookie");
+                                    }
+                                }))
+                .build();
+    }
+}