diff --git a/lib/Controller/AccountController.php b/lib/Controller/AccountController.php
index 663bde760ee071a9224a505dd033342ae7a67909..8f9c849bdeca3fcaa757f7ecf434261f7be3d9ea 100644
--- a/lib/Controller/AccountController.php
+++ b/lib/Controller/AccountController.php
@@ -30,7 +30,7 @@ class AccountController extends Controller {
 	private $session;
 	private $userSession;
 	private $urlGenerator;
-
+	private const SESSION_USERNAME_CHECK = 'username_check_passed';
 	private const CAPTCHA_VERIFIED_CHECK = 'captcha_verified';
 
 	public function __construct(
@@ -99,6 +99,12 @@ class AccountController extends Controller {
 			return $response;
 		}
 
+		if (!$this->session->get(self::SESSION_USERNAME_CHECK)) {
+			$response->setData(['message' => 'Username is already taken.', 'success' => false]);
+			$response->setStatus(400);
+			return $response;
+		}
+
 		$inputData = [
 			'username' => ['value' => $username, 'maxLength' => 30],
 			'displayname' => ['value' => $displayname, 'maxLength' => 30],
@@ -139,7 +145,15 @@ class AccountController extends Controller {
 			$response->setData(['message' => $e->getMessage(), 'success' => false]);
 			$response->setStatus(500);
 		}
+
+		$this->session->remove(self::SESSION_USERNAME_CHECK);
 		$this->session->remove(self::CAPTCHA_VERIFIED_CHECK);
+
+		try {
+			$this->userService->addUsernameToCommonDataStore($username);
+		} catch (Exception $e) {
+			$this->logger->logException($e, ['app' => Application::APP_ID]);
+		}
 		return $response;
 	}
 	/**
@@ -176,9 +190,21 @@ class AccountController extends Controller {
 	public function checkUsernameAvailable(string $username) : DataResponse {
 		$response = new DataResponse();
 		$response->setStatus(400);
-		if (!$this->userService->userExists($username)) {
-			$response->setStatus(200);
+
+		if (empty($username)) {
+			return $response;
+		}
+
+		try {
+			if (!$this->userService->userExists($username) && !$this->userService->isUsernameTaken($username)) {
+				$response->setStatus(200);
+				$this->session->set(self::SESSION_USERNAME_CHECK, true);
+			}
+		} catch (Exception $e) {
+			$this->logger->logException($e, ['app' => Application::APP_ID ]);
+			$response->setStatus(500);
 		}
+
 		return $response;
 	}
 
@@ -208,10 +234,10 @@ class AccountController extends Controller {
 	public function verifyCaptcha(string $captchaInput = '') : DataResponse {
 		$response = new DataResponse();
 		
-		$captchaResult = (string)$this->session->get('captcha_result', '');
+		$captchaResult = (string) $this->session->get(CaptchaService::CAPTCHA_RESULT_KEY, '');
 		$response->setStatus(400);
 		if ($captchaResult === $captchaInput) {
-			$this->session->remove('captcha_result');
+			$this->session->remove(CaptchaService::CAPTCHA_RESULT_KEY);
 			$this->session->set(self::CAPTCHA_VERIFIED_CHECK, true);
 			$response->setStatus(200);
 		}
diff --git a/lib/Service/CaptchaService.php b/lib/Service/CaptchaService.php
index 4bc4245dd51867f16705779c5643762304d51283..1a0ea4b6529162461ffc0d13618cb2a8ad34df4c 100644
--- a/lib/Service/CaptchaService.php
+++ b/lib/Service/CaptchaService.php
@@ -8,11 +8,12 @@ use OCP\ISession;
 
 class CaptchaService {
 	private $session;
-	public const WIDTH = 80;
-	public const HEIGHT = 40;
-	public const NUMBERS = '123456789';
-	public const SYMBOLS = '+-';
-	public const NOISE_LEVEL = 13;
+	private const WIDTH = 80;
+	private const HEIGHT = 40;
+	private const NUMBERS = '123456789';
+	private const SYMBOLS = '+-';
+	private const NOISE_LEVEL = 13;
+	public const CAPTCHA_RESULT_KEY = 'captcha_result';
 
 	public function __construct(ISession $session) {
 		$this->session = $session;
@@ -195,7 +196,7 @@ class CaptchaService {
 	 * @return void
 	 */
 	private function updateSession(float $captchaResult): void {
-		$this->session->set('captcha_result', $captchaResult);
+		$this->session->set(self::CAPTCHA_RESULT_KEY, $captchaResult);
 	}
 
 	
diff --git a/lib/Service/CurlService.php b/lib/Service/CurlService.php
index d7a477fc51e251c3ff991f4f090f324963c7c812..d3b132d500d7368f85a599708f8c41bbf76d3ca0 100644
--- a/lib/Service/CurlService.php
+++ b/lib/Service/CurlService.php
@@ -14,6 +14,8 @@ namespace OCA\EcloudAccounts\Service;
 use Exception;
 
 class CurlService {
+
+	private int $lastStatusCode = 0;
 	/**
 	 * GET alias for request method
 	 *
@@ -44,6 +46,14 @@ class CurlService {
 		return $this->request('DELETE', $url, $params, $headers, $userOptions);
 	}
 
+	/**
+	 * @return int
+	 */
+
+	public function getLastStatusCode() : int {
+		return $this->lastStatusCode;
+	}
+
 
 	/**
 	 * Curl run request
@@ -90,6 +100,9 @@ class CurlService {
 
 		$response = curl_exec($ch);
 
+		$this->lastStatusCode = (int) curl_getinfo($ch, CURLINFO_HTTP_CODE);
+		
+
 		if ($errno = curl_errno($ch)) {
 			var_dump($errno);
 			$errorMessage = curl_strerror($errno);
diff --git a/lib/Service/UserService.php b/lib/Service/UserService.php
index f35b6e6e3d5c59806c85afd844e35908bcc8d07e..dbda65c47ace65ce1a51e215136f085ea952163b 100644
--- a/lib/Service/UserService.php
+++ b/lib/Service/UserService.php
@@ -393,4 +393,59 @@ class UserService {
 		$quota = strval($quota) . ' MB';
 		$user->setQuota($quota);
 	}
+
+	public function isUsernameTaken(string $username) : bool {
+		$commonApiUrl = $this->apiConfig['commonApiUrl'];
+		$commonApiVersion = $this->apiConfig['commonApiVersion'];
+
+		if (!isset($commonApiUrl) || empty($commonApiUrl)) {
+			return false;
+		}
+		$endpoint = $commonApiVersion . '/users/';
+		$url = $commonApiUrl . $endpoint . $username;
+
+		$token = $this->apiConfig['commonServiceToken'];
+		$headers = [
+			"Authorization: Bearer $token"
+		];
+
+		$this->curl->get($url, [], $headers);
+
+		$statusCode = $this->curl->getLastStatusCode();
+		if ($statusCode === 404) {
+			return false;
+		}
+
+		if ($statusCode === 200) {
+			return true;
+		}
+
+		throw new Exception("Error checking if username is taken at common source, status code: " . (string) $statusCode);
+	}
+
+	public function addUsernameToCommonDataStore(string $username) : void {
+		$commonApiUrl = $this->apiConfig['commonApiUrl'];
+		$commonApiVersion = $this->apiConfig['commonApiVersion'];
+
+		if (!isset($commonApiUrl) || empty($commonApiUrl)) {
+			return;
+		}
+		$endpoint = $commonApiVersion . '/users/';
+		$url = $commonApiUrl . $endpoint ;
+		
+		$params = [
+			'username' => $username
+		];
+
+		$token = $this->apiConfig['commonServiceToken'];
+		$headers = [
+			"Authorization: Bearer $token"
+		];
+		
+		$this->curl->post($url, $params, $headers);
+
+		if ($this->curl->getLastStatusCode() !== 200) {
+			throw new Exception('Error adding username ' . $username . ' to common data store');
+		}
+	}
 }
diff --git a/src/signup/RegistrationForm.vue b/src/signup/RegistrationForm.vue
index 3a5f091be282a97fd2f467fa6a1ef26bde636aa8..ff81f3d7da1263e8ab610bd2a27b94a285f35a5f 100644
--- a/src/signup/RegistrationForm.vue
+++ b/src/signup/RegistrationForm.vue
@@ -289,9 +289,9 @@ export default {
 				}
 			}
 		},
-		submitRegistrationForm() {
+		async submitRegistrationForm() {
 			this.validateForm(['displayname', 'username', 'password', 'repassword', 'termsandservices'])
-			this.checkUsername()
+			await this.checkUsername()
 			const isFormValid = Object.values(this.validation).every(value => !value)
 
 			if (isFormValid) {