wip: Generate and configure OpenAPI spec

- Create two (non-functioning) demo endpoints to check the swagger UI with
- Configure Jackson to only serialize specific attributes
- Configure SpringDoc so that only attributes known to Jackson are shown
- Add some shortcut annotations for Json formatting

src/main/java/de/mlessmann/certassist/config/JacksonConfiguration.java

@@ -0,0 +1,35 @@
+package de.mlessmann.certassist.config;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.PropertyAccessor;
+import com.fasterxml.jackson.databind.MapperFeature;
+import org.springframework.boot.autoconfigure.jackson.Jackson2ObjectMapperBuilderCustomizer;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+@Configuration
+public class JacksonConfiguration {
+
+    /**
+     * Customizes the objectMapper so that ONLY specifically annotated fields are serialized.
+     * Other fields MUST NOT be serialized since they may contain sensitive information!
+     */
+    @Bean
+    public Jackson2ObjectMapperBuilderCustomizer customizeObjectMapper() {
+        return builder -> builder
+                .featuresToDisable(
+                        MapperFeature.AUTO_DETECT_FIELDS,
+                        MapperFeature.AUTO_DETECT_GETTERS,
+                        MapperFeature.AUTO_DETECT_IS_GETTERS
+                )
+                .serializationInclusion(JsonInclude.Include.NON_EMPTY)
+                .visibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE)
+                .visibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.NONE)
+                .visibility(PropertyAccessor.GETTER, JsonAutoDetect.Visibility.NONE)
+                .visibility(PropertyAccessor.IS_GETTER, JsonAutoDetect.Visibility.NONE)
+                .visibility(PropertyAccessor.SETTER, JsonAutoDetect.Visibility.PUBLIC_ONLY)
+                .visibility(PropertyAccessor.CREATOR, JsonAutoDetect.Visibility.PUBLIC_ONLY)
+                .build();
+    }
+}