diff --git a/src/Enum/UpsertBehaviorEnum.php b/src/Enum/UpsertBehaviorEnum.php
new file mode 100644
index 00000000..649101fb
--- /dev/null
+++ b/src/Enum/UpsertBehaviorEnum.php
@@ -0,0 +1,32 @@
+<?php
+/**
+ * Copyright 2018 AlexaCRM
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+ * associated documentation files (the "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+ * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+ * PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
+ * OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+namespace AlexaCRM\Enum;
+
+/**
+ * Specifies the behavior for an Upsert operation.
+ */
+enum UpsertBehaviorEnum: int {
+
+    case CreateOrUpdate = 0;
+    case PreventUpdate = 1;
+    case PreventCreate = 2;
+}
diff --git a/src/WebAPI/Client.php b/src/WebAPI/Client.php
index bd2b1c65..a9b7d23f 100644
--- a/src/WebAPI/Client.php
+++ b/src/WebAPI/Client.php
@@ -21,6 +21,7 @@
 
 namespace AlexaCRM\WebAPI;
 
+use AlexaCRM\Enum\UpsertBehaviorEnum;
 use AlexaCRM\WebAPI\OData\AuthenticationException;
 use AlexaCRM\WebAPI\OData\Client as ODataClient;
 use AlexaCRM\WebAPI\OData\EntityNotSupportedException;
@@ -49,6 +50,12 @@ class Client implements IOrganizationService {
      */
     protected ODataClient $client;
 
+    protected ?string $MSCRMCallerID;
+
+    protected ?string $callerObjectId;
+
+    protected UpsertBehaviorEnum $upsertBehavior;
+
     /**
      * Client constructor.
      *
@@ -56,6 +63,7 @@ class Client implements IOrganizationService {
      */
     public function __construct( ODataClient $client ) {
         $this->client = $client;
+        $this->upsertBehavior = UpsertBehaviorEnum::CreateOrUpdate;
     }
 
     /**
@@ -107,7 +115,7 @@ public function Create( Entity $entity ): string {
             $translatedData = $serializer->serializeEntity( $entity );
 
             $collectionName = $this->client->getMetadata()->getEntitySetName( $entity->LogicalName );
-
+            $this->updateWebApiHeaderRequest();
             $responseId = $this->client->create( $collectionName, $translatedData );
 
             $entity->getAttributeState()->reset();
@@ -233,9 +241,8 @@ public function Retrieve( string $entityName, string $entityId, ColumnSet $colum
             $response = $this->client->getRecord( $collectionName, $entityId, $options );
 
             $serializer = new SerializationHelper( $this->client );
-            $entity = $serializer->deserializeEntity( $response, new EntityReference( $entityName, $entityId ) );
 
-            return $entity;
+            return $serializer->deserializeEntity( $response, new EntityReference( $entityName, $entityId ) );
         } catch ( ODataException $e ) {
             if ( $e->getCode() === 404 ) {
                 return null;
@@ -388,7 +395,7 @@ protected function retrieveViaQueryByAttribute( QueryByAttribute $query ): Entit
                         $queryValue = "'{$value}'";
                         break;
                     case is_bool( $value ):
-                        $queryValue = $value? 'true' : 'false';
+                        $queryValue = $value ? 'true' : 'false';
                         break;
                     case $value === null:
                         $queryValue = 'null';
@@ -491,6 +498,30 @@ protected function retrieveViaQueryByAttribute( QueryByAttribute $query ): Entit
         }
     }
 
+    /**
+     * Updating WebApi Request Headers
+     *
+     * @return void
+     */
+    private function updateWebApiHeaderRequest(): void {
+        switch ( $this->upsertBehavior ) {
+            case UpsertBehaviorEnum::PreventCreate:
+                $this->client->setWebApiHeaderByName( "If-Match", "*" );
+                break;
+            case UpsertBehaviorEnum::PreventUpdate:
+                $this->client->setWebApiHeaderByName( "If-None-Match", "*" );
+                break;
+            default:
+                break;
+        }
+
+        if ( $this->callerObjectId !== null ) {
+            $this->client->setWebApiHeaderByName( 'CallerObjectId', $this->callerObjectId );
+        } elseif ( $this->MSCRMCallerID !== null ) {
+            $this->client->setWebApiHeaderByName( 'MSCRMCallerID', $this->MSCRMCallerID );
+        }
+    }
+
     /**
      * Updates an existing record.
      *
@@ -508,6 +539,7 @@ public function Update( Entity $entity ): void {
 
             $collectionName = $this->client->getMetadata()->getEntitySetName( $entity->LogicalName );
 
+            $this->updateWebApiHeaderRequest();
             $this->client->update( $collectionName, $entity->Id, $translatedData );
 
             $entity->getAttributeState()->reset();
@@ -536,4 +568,34 @@ public function getCachePool(): CacheItemPoolInterface {
         return $this->client->getCachePool();
     }
 
+    public function getMSCRMCallerID(): ?string {
+        return $this->MSCRMCallerID;
+    }
+
+    public function setMSCRMCallerID( ?string $MSCRMCallerID ): void {
+        try {
+            //search Microsoft Entra ID object ID
+            $entity = $this->Retrieve( 'systemuser', $MSCRMCallerID, new ColumnSet( [ 'azureactivedirectoryobjectid' ] ) );
+            $this->callerObjectId = $entity?->Attributes['azureactivedirectoryobjectid'];
+        } catch ( Exception ) {
+        }
+        $this->MSCRMCallerID = $MSCRMCallerID;
+    }
+
+    public function getCallerObjectId(): ?string {
+        return $this->callerObjectId;
+    }
+
+    public function setCallerObjectId( ?string $callerObjectId ): void {
+        $this->callerObjectId = $callerObjectId;
+    }
+
+    public function getUpsertBehavior(): UpsertBehaviorEnum {
+        return $this->upsertBehavior;
+    }
+
+    public function setUpsertBehavior( UpsertBehaviorEnum $upsertBehavior ): void {
+        $this->upsertBehavior = $upsertBehavior;
+    }
+
 }
diff --git a/src/WebAPI/OData/Client.php b/src/WebAPI/OData/Client.php
index b5ebf271..94fcd649 100644
--- a/src/WebAPI/OData/Client.php
+++ b/src/WebAPI/OData/Client.php
@@ -34,6 +34,7 @@
 use GuzzleHttp\Exception\RequestException;
 use GuzzleHttp\HandlerStack;
 use Psr\Cache\CacheItemPoolInterface;
+use Psr\Cache\InvalidArgumentException;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Log\LoggerInterface;
 
@@ -66,6 +67,13 @@ class Client {
      */
     protected array $middlewares = [];
 
+    /**
+     * header to Web API request
+     *
+     * @var array
+     */
+    protected array $webApiHeaders = [];
+
     /**
      * Client constructor.
      *
@@ -129,8 +137,11 @@ public function getHttpClient(): HttpClient {
     /**
      * Retrieves OData Service Metadata.
      *
+     * @return Metadata
      * @throws AuthenticationException
+     * @throws GuzzleException
      * @throws TransportException
+     * @throws InvalidArgumentException
      */
     public function getMetadata(): Metadata {
         if ( $this->metadata instanceof Metadata ) {
@@ -178,6 +189,34 @@ public function getMetadata(): Metadata {
         return $this->metadata;
     }
 
+    /**
+     * Get header for Web Api Request
+     *
+     * @param array|null $headers
+     * @param string|null $method
+     *
+     * @return array
+     */
+    private function getRequestHeaders( ?array $headers = [], ?string $method = 'GET' ): array {
+        if ( in_array( $method, [ 'POST', 'PATCH' ] ) ) {
+            $headers = array_merge( [ 'Content-Type' => 'application/json' ], $headers );
+        }
+
+        //Odata/Client/Setting more important than the headers in the request
+        if ( $this->settings->callerObjectId || $this->settings->callerID ) {
+            $this->unsetWebApiHeaderByName( 'CallerObjectId' );
+            $this->unsetWebApiHeaderByName( 'MSCRMCallerID' );
+        }
+
+        if ( $this->settings->callerObjectId !== null ) {
+            $headers = array_merge( [ 'CallerObjectId' => $this->settings->callerObjectId ], $headers );
+        } elseif ( $this->settings->callerID !== null ) {
+            $headers = array_merge( [ 'MSCRMCallerID' => $this->settings->callerID ], $headers );
+        }
+
+        return $headers;
+    }
+
     /**
      * @param string $method
      * @param string $url
@@ -190,13 +229,7 @@ public function getMetadata(): Metadata {
      * @throws TransportException
      */
     private function doRequest( string $method, string $url, $data = null, array $headers = [] ): ResponseInterface {
-        if ( in_array( $method, [ 'POST', 'PATCH' ] ) ) {
-            $headers = array_merge( [ 'Content-Type' => 'application/json' ], $headers );
-        }
-
-        if ( $this->settings->callerID !== null ) {
-            $headers = array_merge( [ 'MSCRMCallerID' => '$this->settings->callerID' ], $headers );
-        }
+        $headers = $this->getRequestHeaders( $headers, $method );
 
         try {
             $payload = [
@@ -577,7 +610,7 @@ public function associate(
         string $fromEntityId,
         string $navProperty,
         string $toEntityCollection,
-        string $toEntityId
+        string $toEntityId,
     ): void {
         $url = sprintf( '%s%s(%s)/%s/$ref', $this->settings->getEndpointURI(), $fromEntityCollection, $fromEntityId, $navProperty );
         $data = [ Annotation::ODATA_ID => sprintf( '%s%s(%s)', $this->settings->getEndpointURI(), $toEntityCollection, $toEntityId ) ];
@@ -600,9 +633,10 @@ public function disassociate(
         string $fromEntityId,
         string $navProperty,
         string $toEntityCollection,
-        string $toEntityId
+        string $toEntityId,
     ): void {
-        $url = sprintf( '%s%s(%s)/%s/$ref?$id=%s%s(%s)', $this->settings->getEndpointURI(), $fromEntityCollection, $fromEntityId, $navProperty, $this->settings->getEndpointURI(), $toEntityCollection, $toEntityId );
+        $url = sprintf( '%s%s(%s)/%s/$ref?$id=%s%s(%s)', $this->settings->getEndpointURI(), $fromEntityCollection, $fromEntityId, $navProperty, $this->settings->getEndpointURI(),
+            $toEntityCollection, $toEntityId );
         $this->doRequest( 'DELETE', $url );
     }
 
@@ -795,4 +829,20 @@ protected static function getEntityId( ResponseInterface $response ): ?string {
         return $id;
     }
 
+    public function getWebApiHeaderByName( $headerName ): array {
+        return $this?->webApiHeaders[ $headerName ];
+    }
+
+    public function unsetWebApiHeaderByName( $headerName ): void {
+        unset( $this->webApiHeaders[ $headerName ] );
+    }
+
+    public function setWebApiHeaderByName( $headerName, $headerValue ): void {
+        $this->webApiHeaders[ $headerName ] = $headerValue;
+    }
+
+    public function getWebApiHeaders(): array {
+        return $this->webApiHeaders;
+    }
+
 }
diff --git a/src/WebAPI/OData/Settings.php b/src/WebAPI/OData/Settings.php
index 1fe5dd6b..ff8da4eb 100644
--- a/src/WebAPI/OData/Settings.php
+++ b/src/WebAPI/OData/Settings.php
@@ -75,12 +75,19 @@ abstract class Settings implements LoggerAwareInterface {
     public LoggerInterface $logger;
 
     /**
-     * ID of the user to impersonate during calls.
-     *
+     * ID of the user (systemuserid) to impersonate during calls.
+     * @deprecated
      * Null value means impersonation is not performed.
      */
     public ?string $callerID = null;
 
+    /**
+     * Microsoft Entra ID object ID (Azure AD Object ID) - azureactivedirectoryobjectid
+     *
+     * Null value means impersonation is not performed.
+     */
+    public ?string $callerObjectId = null;
+
     /**
      * Settings constructor.
      */