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diff --git a/apps/files_external/lib/Config/SimpleSubstitutionTrait.php b/apps/files_external/lib/Config/SimpleSubstitutionTrait.php
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+++ b/apps/files_external/lib/Config/SimpleSubstitutionTrait.php
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+<?php
+/**
+ * @copyright Copyright (c) 2019 Arthur Schiwon <blizzz@arthur-schiwon.de>
+ *
+ * @author Arthur Schiwon <blizzz@arthur-schiwon.de>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\Files_External\Config;
+
+/**
+ * Trait SimpleSubstitutionTrait
+ *
+ * @package OCA\Files_External\Config
+ * @since 16.0.0
+ */
+trait SimpleSubstitutionTrait {
+	/**
+	 * @var string the placeholder without $ prefix
+	 * @since 16.0.0
+	 */
+	private $placeholder;
+
+	/** @var string */
+	protected $sanitizedPlaceholder;
+
+	/**
+	 * @param mixed $optionValue
+	 * @param string $replacement
+	 * @return mixed
+	 * @since 16.0.0
+	 */
+	private function processInput($optionValue, string $replacement) {
+		$this->checkPlaceholder();
+		if (is_array($optionValue)) {
+			foreach ($optionValue as &$value) {
+				$value = $this->substituteIfString($value, $replacement);
+			}
+		} else {
+			$optionValue = $this->substituteIfString($optionValue, $replacement);
+		}
+		return $optionValue;
+	}
+
+	/**
+	 * @throws \RuntimeException
+	 */
+	protected function checkPlaceholder(): void {
+		$this->sanitizedPlaceholder = trim(strtolower($this->placeholder));
+		if(!(bool)\preg_match('/^[a-z0-9]*$/', $this->sanitizedPlaceholder)) {
+			throw new \RuntimeException(sprintf(
+				'Invalid placeholder %s, only [a-z0-9] are allowed', $this->sanitizedPlaceholder
+			));
+		}
+		if($this->sanitizedPlaceholder === '') {
+			throw new \RuntimeException('Invalid empty placeholder');
+		}
+	}
+
+	/**
+	 * @param mixed $value
+	 * @param string $replacement
+	 * @return mixed
+	 */
+	protected function substituteIfString($value, string $replacement) {
+		if(is_string($value)) {
+			return str_ireplace('$' . $this->sanitizedPlaceholder, $replacement, $value);
+		}
+		return $value;
+	}
+}