diff --git a/pom.xml b/pom.xml
index 70ab604..8f2b681 100644
--- a/pom.xml
+++ b/pom.xml
@@ -37,6 +37,7 @@
 
     <cleanthat.version>2.17</cleanthat.version>
     <error-prone.version>2.24.1</error-prone.version>
+    <google-java-format.version>1.19.2</google-java-format.version>
 
     <maven-clean-plugin.version>3.3.2</maven-clean-plugin.version>
     <maven-compiler-plugin.version>3.12.1</maven-compiler-plugin.version>
diff --git a/src/main/java/tech/stackable/hadoop/StackableGroupMapper.java b/src/main/java/tech/stackable/hadoop/StackableGroupMapper.java
index b1ee34a..f4bb2f4 100644
--- a/src/main/java/tech/stackable/hadoop/StackableGroupMapper.java
+++ b/src/main/java/tech/stackable/hadoop/StackableGroupMapper.java
@@ -4,29 +4,23 @@
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import java.io.IOException;
 import java.net.URI;
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 import java.util.Objects;
-
-import com.fasterxml.jackson.databind.type.TypeFactory;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.security.GroupMappingServiceProvider;
+import org.apache.hadoop.security.UserGroupInformation;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 public class StackableGroupMapper implements GroupMappingServiceProvider {
 
-  private static final Logger LOG = LoggerFactory.getLogger(StackableGroupMapper.class);
-
   public static final String OPA_MAPPING_URL_PROP = "hadoop.security.group.mapping.opa.policy.url";
-  // response base field: see https://www.openpolicyagent.org/docs/latest/rest-api/#response-message
-  private static final String OPA_RESULT_FIELD = "result";
-
+  private static final Logger LOG = LoggerFactory.getLogger(StackableGroupMapper.class);
   private final HttpClient httpClient = HttpClient.newHttpClient();
   private final ObjectMapper json;
   private URI opaUri;
@@ -59,21 +53,36 @@ public StackableGroupMapper() {
             .setSerializationInclusion(JsonInclude.Include.NON_NULL);
   }
 
-  private static class OpaQueryResult {
-    public List<String> result;
-  }
-
   /**
-   * Returns list of groups for a user.
+   * Returns list of groups for a user. Internally Hadoop will pass the short name to this function,
+   * but this prevents us from effectively separating users with the same names but with different
+   * kerberos principals. For this reason the user name is extracted from the UserGroupInformation
+   * instead (giving us the full name), defaulting to the original name if this is not possible.
    *
-   * @param user get groups for this user
+   * @param user get groups from the associated user group information for this user
    * @return list of groups for a given user
    */
   @Override
   public List<String> getGroups(String user) {
     LOG.info("Calling StackableGroupMapper.getGroups for user \"{}\"", user);
 
-    OpaGroupsQuery query = new OpaGroupsQuery(new OpaGroupsQuery.OpaGroupsQueryInput(user));
+    String workingUser = user;
+    try {
+      UserGroupInformation currentUser = UserGroupInformation.getCurrentUser();
+      LOG.debug(
+          "Current user [{}] with user-name [{}] and short-name [{}]",
+          currentUser,
+          currentUser.getUserName(),
+          currentUser.getShortUserName());
+      workingUser = currentUser.getUserName();
+    } catch (IOException e) {
+      LOG.warn(
+          "Unable to extract name from UserGroupInformation, defaulting to \"{}\": {}",
+          user,
+          e.getMessage());
+    }
+
+    OpaGroupsQuery query = new OpaGroupsQuery(new OpaGroupsQuery.OpaGroupsQueryInput(workingUser));
 
     String body;
     try {
@@ -115,7 +124,7 @@ public List<String> getGroups(String user) {
     }
     List<String> groups = result.result;
 
-    LOG.debug("Groups for \"{}\": {}", user, groups);
+    LOG.debug("Groups for \"{}\": {}", workingUser, groups);
 
     return groups;
   }
@@ -139,4 +148,8 @@ public void cacheGroupsAdd(List<String> groups) {
         "ignoring cacheGroupsAdd for groups [{}]: caching should be provided by the policy provider",
         groups);
   }
+
+  private static class OpaQueryResult {
+    public List<String> result;
+  }
 }