diff --git a/.phpcs.xml.dist b/.phpcs.xml.dist
index f3d3852ed..ebab20d90 100644
--- a/.phpcs.xml.dist
+++ b/.phpcs.xml.dist
@@ -206,6 +206,13 @@
 		</properties>
 	</rule>
 
+	<!-- In contrast to WPCS (40%), we allow a slightly higher percentage. -->
+	<rule ref="Squiz.PHP.CommentedOutCode">
+		<properties>
+			<property name="maxPercentage" value="50"/>
+		</properties>
+	</rule>
+
 
 	<!--
 	#############################################################################
diff --git a/src/Utility/InputValidator.php b/src/Utility/InputValidator.php
index 25d849b23..4ca0324f6 100644
--- a/src/Utility/InputValidator.php
+++ b/src/Utility/InputValidator.php
@@ -109,4 +109,27 @@ public static function is_curl_handle($input) {
 
 		return false;
 	}
+
+	/**
+	 * Verify that a received input parameter is a valid "token name" according to the
+	 * specification in RFC 2616 (HTTP/1.1).
+	 *
+	 * The short version is: 1 or more ASCII characters, CTRL chars and separators not allowed.
+	 * For the long version, see the specs in the RFC.
+	 *
+	 * @link https://datatracker.ietf.org/doc/html/rfc2616#section-2.2
+	 *
+	 * @since 2.1.0
+	 *
+	 * @param mixed $input Input parameter to verify.
+	 *
+	 * @return bool
+	 */
+	public static function is_valid_rfc2616_token($input) {
+		if (!is_int($input) && !is_string($input)) {
+			return false;
+		}
+
+		return preg_match('@^[0-9A-Za-z!#$%&\'*+.^_`|~-]+$@', $input) === 1;
+	}
 }
diff --git a/tests/Utility/InputValidator/IsValidRfc2616TokenTest.php b/tests/Utility/InputValidator/IsValidRfc2616TokenTest.php
new file mode 100644
index 000000000..bd4e02cb7
--- /dev/null
+++ b/tests/Utility/InputValidator/IsValidRfc2616TokenTest.php
@@ -0,0 +1,177 @@
+<?php
+
+namespace WpOrg\Requests\Tests\Utility\InputValidator;
+
+use WpOrg\Requests\Tests\TestCase;
+use WpOrg\Requests\Tests\TypeProviderHelper;
+use WpOrg\Requests\Utility\InputValidator;
+
+/**
+ * @covers \WpOrg\Requests\Utility\InputValidator::is_valid_rfc2616_token
+ */
+final class IsValidRfc2616TokenTest extends TestCase {
+
+	/**
+	 * Test whether a received input parameter is correctly identified as a valid RFC 2616 token.
+	 *
+	 * @dataProvider dataValidIntegers
+	 * @dataProvider dataValidStrings
+	 *
+	 * @param mixed $input Input parameter to verify.
+	 *
+	 * @return void
+	 */
+	public function testValid($input) {
+		$this->assertTrue(InputValidator::is_valid_rfc2616_token($input));
+	}
+
+	/**
+	 * Data Provider.
+	 *
+	 * @return array
+	 */
+	public static function dataValidIntegers() {
+		return TypeProviderHelper::getSelection(TypeProviderHelper::GROUP_INT);
+	}
+
+	/**
+	 * Data Provider.
+	 *
+	 * Valid strings are valid tokens as per RFC 2616 section 2.2:
+	 * token = 1*<any CHAR except CTLs or separators>
+	 *
+	 * @return array
+	 */
+	public static function dataValidStrings() {
+
+		return [
+			'string containing all valid token characters' => [
+				'input' => implode('', self::getValidTokenCharacters()),
+			],
+			'string with a typical cookie name' => [
+				'input' => 'requests-testcookie',
+			],
+		];
+	}
+
+	/**
+	 * Test whether a received input parameter is correctly identified as NOT a valid RFC 2616 token.
+	 *
+	 * @dataProvider dataInvalidTypes
+	 * @dataProvider dataInvalidValues
+	 *
+	 * @param mixed $input Input parameter to verify.
+	 *
+	 * @return void
+	 */
+	public function testInvalid($input) {
+		$this->assertFalse(InputValidator::is_valid_rfc2616_token($input));
+	}
+
+	/**
+	 * Data Provider for invalid data types.
+	 *
+	 * @return array
+	 */
+	public static function dataInvalidTypes() {
+		return TypeProviderHelper::getAllExcept(TypeProviderHelper::GROUP_INT, TypeProviderHelper::GROUP_STRING);
+	}
+
+	/**
+	 * Data Provider for valid data types containing invalid values.
+	 *
+	 * @return array
+	 */
+	public static function dataInvalidValues() {
+		$all_control = chr(127); // DEL.
+		for ($char = 0; $char <= 31; $char++) {
+			$all_control .= chr($char);
+		}
+
+		$invalid_ascii_characters = array_diff(
+			array_map('chr', range(0, 127)),
+			self::getValidTokenCharacters()
+		);
+
+		return [
+			'empty string' => [
+				'input' => '',
+			],
+			'string containing only control characters / all control characters' => [
+				'input' => $all_control,
+			],
+			'string containing control character at start' => [
+				'input' => chr(6) . 'some text',
+			],
+			'string containing control characters in text' => [
+				'input' => "some\ntext\rwith\tcontrol\echaracters\fin\vit",
+			],
+			'string containing control character at end' => [
+				'input' => 'some text' . chr(127),
+			],
+			'string containing only separator characters / all separator characters' => [
+				'input' => '()<>@,;:\\"/[]?={} 	',
+			],
+			'string containing separator character at start' => [
+				'input' => '=value',
+			],
+			'string containing separator characters in text' => [
+				'input' => 'words "with" spaces and quotes',
+			],
+			'string containing separator character at end' => [
+				'input' => 'punctuated;',
+			],
+			'string containing separator characters - leading and trailing whitespace' => [
+				'input' => '	words    ',
+			],
+			'string containing non-ascii characters - Iñtërnâtiônàlizætiøn' => [
+				'input' => 'Iñtërnâtiônàlizætiøn',
+			],
+			'string containing non-ascii characters - ௫' => [
+				'input' => '௫', // Tamil digit five.
+			],
+			'string containing all invalid ASCII characters' => [
+				'input' => implode('', $invalid_ascii_characters),
+			],
+		];
+	}
+
+	/**
+	 * Get an array of valid RFC 2616 token characters.
+	 *
+	 * Valid token as per RFC 2616 section 2.2:
+	 * token = 1*<any CHAR except CTLs or separators>
+	 *
+	 * Disabling PHPCS checks for consistency with RFC 2616:
+	 * @phpcs:disable WordPress.Arrays.ArrayDeclarationSpacing.ArrayItemNoNewLine
+	 *
+	 * @return array<string>
+	 */
+	private static function getValidTokenCharacters() {
+		// CHAR = <any US-ASCII character (octets 0 - 127)>
+		$rfc_char = array_map('chr', range(0, 127));
+
+		// CTL = <any US-ASCII control character (octets 0 - 31) and DEL (127)>
+		$rfc_ctl = array_map('chr', array_merge(range(0, 31), [127]));
+
+		// SP = <US-ASCII SP, space (32)>
+		$rfc_sp = chr(32);
+
+		// HT = <US-ASCII HT, horizontal-tab (9)>
+		$rfc_ht = chr(9);
+
+		// Separators = "(" | ")" | "<" | ">" | "@"
+		//            | "," | ";" | ":" | "\" | <">
+		//            | "/" | "[" | "]" | "?" | "="
+		//            | "{" | "}" | SP | HT
+		$rfc_separators = [
+			'(', ')', '<', '>', '@',
+			',', ';', ':', '\\', '"',
+			'/', '[', ']', '?', '=',
+			'{', '}', $rfc_sp, $rfc_ht,
+		];
+
+		// Token characters = <any CHAR except CTLs or separators>
+		return array_diff($rfc_char, $rfc_ctl, $rfc_separators);
+	}
+}