Clear realpath cache when reading the token from file (#901)

* Apply same fix as aws/aws-sdk-php#2043

* Fix CS

* Add intermediate variables to save on duplicate function calls

* Update src/Core/src/Credentials/WebIdentityProvider.php

Co-authored-by: Tobias Nyholm <tobias.nyholm@gmail.com>

Author: Jean85

src/Credentials/WebIdentityProvider.php

@@ -89,9 +89,7 @@ private function getCredentialsFromRole(string $roleArn, string $tokenFile, ?str
         }
 
         try {
-            if (false === $token = file_get_contents($tokenFile)) {
-                throw new RuntimeException('failed to read data');
-            }
+            $token = $this->getTokenFileContent($tokenFile);
         } catch (\Exception $e) {
             $this->logger->warning('"Error reading WebIdentityTokenFile "{tokenFile}.', ['tokenFile' => $tokenFile, 'exception' => $e]);
 
@@ -122,4 +120,26 @@ private function getCredentialsFromRole(string $roleArn, string $tokenFile, ?str
             Credentials::adjustExpireDate($credentials->getExpiration(), $this->getDateFromResult($result))
         );
     }
+
+    /**
+     * @see https://github.com/async-aws/aws/issues/900
+     * @see https://github.com/aws/aws-sdk-php/issues/2014
+     * @see https://github.com/aws/aws-sdk-php/pull/2043
+     */
+    private function getTokenFileContent(string $tokenFile): string
+    {
+        if (!file_exists($tokenFile)) {
+            $tokenDir = \dirname($tokenFile);
+            $tokenLink = readlink($tokenFile);
+            clearstatcache(true, $tokenDir . \DIRECTORY_SEPARATOR . $tokenLink);
+            clearstatcache(true, $tokenDir . \DIRECTORY_SEPARATOR . \dirname($tokenLink));
+            clearstatcache(true, $tokenFile);
+        }
+
+        if (false === $token = file_get_contents($tokenFile)) {
+            throw new RuntimeException('Failed to read data');
+        }
+
+        return $token;
+    }
 }