Add way to iterate config properties in ConfigSourceContext.

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

@@ -1,5 +1,7 @@
 package io.smallrye.config;
 
+import java.util.Iterator;
+
 import io.smallrye.common.annotation.Experimental;
 
 /**
@@ -8,4 +10,6 @@
 @Experimental("ConfigSource API Enhancements")
 public interface ConfigSourceContext {
     ConfigValue getValue(String name);
+
+    Iterator<String> iterateNames();
 }

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

@@ -28,6 +28,7 @@
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.ListIterator;
 import java.util.Map;
@@ -329,7 +330,18 @@ private static class ConfigSources implements Serializable {
                     .collect(toList());
 
             final List<ConfigSourceInterceptorWithPriority> lateInterceptors = lateInitSources.stream()
-                    .flatMap(configurableConfigSource -> configurableConfigSource.getConfigSources(initChain::proceed).stream())
+                    .flatMap(configurableConfigSource -> configurableConfigSource.getConfigSources(
+                            new ConfigSourceContext() {
+                                @Override
+                                public ConfigValue getValue(final String name) {
+                                    return initChain.proceed(name);
+                                }
+
+                                @Override
+                                public Iterator<String> iterateNames() {
+                                    return initChain.iterateNames();
+                                }
+                            }).stream())
                     .map(ConfigSourceInterceptorWithPriority::new)
                     .collect(toList());
 

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

@@ -3,6 +3,7 @@
 import static java.util.stream.Collectors.toList;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.OptionalInt;
@@ -91,4 +92,33 @@ public OptionalInt getPriority() {
         assertEquals("1234", config.getRawValue("any"));
         assertEquals("test", config.getConfigValue("any").getConfigSourceName());
     }
+
+    @Test
+    void iterate() {
+        final SmallRyeConfig config = new SmallRyeConfigBuilder()
+                .addDefaultSources()
+                .addDefaultInterceptors()
+                .withSources(KeyValuesConfigSource.config("smallrye.prop", "1", "smallrye.another", "2", "mp.prop", "1"))
+                .withSources(new ConfigurableConfigSource(new ConfigSourceFactory() {
+                    @Override
+                    public ConfigSource getConfigSource(final ConfigSourceContext context) {
+                        Map<String, String> properties = new HashMap<>();
+                        context.iterateNames().forEachRemaining(s -> {
+                            if (s.startsWith("smallrye")) {
+                                properties.put(s, "1234");
+                            }
+                        });
+                        return KeyValuesConfigSource.config(properties);
+                    }
+
+                    @Override
+                    public OptionalInt getPriority() {
+                        return OptionalInt.of(1000);
+                    }
+                })).build();
+
+        assertEquals("1234", config.getRawValue("smallrye.prop"));
+        assertEquals("1234", config.getRawValue("smallrye.another"));
+        assertEquals("1", config.getRawValue("mp.prop"));
+    }
 }