import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.TreeNode;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.databind.node.ArrayNode;
import io.vertx.core.MultiMap;
import io.vertx.core.http.CaseInsensitiveHeaders;

import java.io.IOException;


public class CaseInsensitiveHeadersDeserializer extends StdDeserializer<MultiMap> {

    protected CaseInsensitiveHeadersDeserializer() {
        super(MultiMap.class);
    }

    @Override
    public MultiMap deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        CaseInsensitiveHeaders headers = new CaseInsensitiveHeaders();
        TreeNode tree = p.readValueAsTree();
        if (tree.isArray()){
            ArrayNode array = (ArrayNode)tree;
            array.forEach(item->{
                item.fields().forEachRemaining(f->{
                    headers.add(f.getKey(), f.getValue().asText());
                });
            });
        }
        return headers;
    }

}

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
import io.vertx.core.MultiMap;

import java.io.IOException;


public class CaseInsensitiveHeadersSerializer extends StdSerializer<MultiMap> {

    protected CaseInsensitiveHeadersSerializer() {
        super(MultiMap.class);
    }

    @Override
    public void serialize(MultiMap value, JsonGenerator gen, SerializerProvider provider) throws IOException {
        gen.writeStartArray();
        value.forEach(v -> {
            try {
                gen.writeObject(v);
            } catch (IOException e) {
                e.printStackTrace();
            }
        });
        gen.writeEndArray();
    }
}

...
    @JsonSerialize(using = CaseInsensitiveHeadersSerializer.class)
    @JsonDeserialize(using = CaseInsensitiveHeadersDeserializer.class)
    private MultiMap commonHeaders = new CaseInsensitiveHeaders();
...

JsonObject configObject = new JsonObject();
configObject.put("headers", Json.encode(myHeaders));