diff --git a/classes/element.registry.php b/classes/element.registry.php
index c33e56524..d564b6331 100644
--- a/classes/element.registry.php
+++ b/classes/element.registry.php
@@ -20,6 +20,9 @@
     'http://eduid.cz/schema/metadata/1.0' => [
         'RepublishRequest' => '\SimpleSAML\SAML2\XML\emd\RepublishRequest',
     ],
+    'urn:mace:surf.nl:stepup:gssp-extensions' => [
+        'UserAttributes' => '\SimpleSAML\SAML2\XML\gssp\UserAttributes',
+    ],
     'urn:oasis:names:tc:SAML:2.0:metadata' => [
         'AdditionalMetadataLocation' => '\SimpleSAML\SAML2\XML\md\AdditionalMetadataLocation',
         'AffiliateMember' => '\SimpleSAML\SAML2\XML\md\AffiliateMember',
diff --git a/resources/schemas/gssp-extensions.xsd b/resources/schemas/gssp-extensions.xsd
new file mode 100644
index 000000000..c5536e60e
--- /dev/null
+++ b/resources/schemas/gssp-extensions.xsd
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
+    targetNamespace="urn:mace:surf.nl:stepup:gssp-extensions"
+    xmlns:gssp="urn:mace:surf.nl:stepup:gssp-extensions"
+    xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" 
+    elementFormDefault="unqualified"
+    attributeFormDefault="unqualified" 
+    version="1.0">
+    <xs:import namespace="urn:oasis:names:tc:SAML:2.0:assertion"
+        schemaLocation="saml-schema-assertion-2.0.xsd"/>
+    <xs:annotation>
+        <xs:documentation>
+            SAML Extension for use in the GSSP protocol: https://github.com/OpenConext/Stepup-Gateway/blob/develop/docs/GSSP.md
+            Version 1.0:
+            - Define UserAttributes element for use in AuthnRequest during GSSP enrollemnt 
+        </xs:documentation>
+    </xs:annotation>
+    <xs:element name="UserAttributes" type="gssp:UserAttributesType"/>
+    <xs:complexType name="UserAttributesType">
+        <xs:sequence>
+            <xs:element ref="saml:Attribute" minOccurs="1" maxOccurs="unbounded"/>
+        </xs:sequence>
+    </xs:complexType>
+</xs:schema>
diff --git a/src/Constants.php b/src/Constants.php
index ac884ff07..c8e02e553 100644
--- a/src/Constants.php
+++ b/src/Constants.php
@@ -241,6 +241,11 @@ class Constants extends \SimpleSAML\XMLSecurity\Constants
      */
     public const string NS_EMD = 'http://eduid.cz/schema/metadata/1.0';
 
+    /**
+     * The namespace for the GSSP-extensions.
+     */
+    public const string NS_GSSP = 'urn:mace:surf.nl:stepup:gssp-extensions';
+
     /**
      * The namespace for the SAML 2 HoK Web Browser SSO Profile.
      */
diff --git a/src/XML/gssp/AbstractGsspElement.php b/src/XML/gssp/AbstractGsspElement.php
new file mode 100644
index 000000000..428ed5abb
--- /dev/null
+++ b/src/XML/gssp/AbstractGsspElement.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\SAML2\XML\gssp;
+
+use SimpleSAML\SAML2\Constants as C;
+use SimpleSAML\XML\AbstractElement;
+
+/**
+ * Abstract class to be implemented by all the classes in this namespace
+ *
+ * @package simplesamlphp/saml2
+ */
+abstract class AbstractGsspElement extends AbstractElement
+{
+    public const string NS = C::NS_GSSP;
+
+    public const string NS_PREFIX = 'gssp';
+
+    public const string SCHEMA = 'resources/schemas/gssp-extensions.xsd';
+}
diff --git a/src/XML/gssp/UserAttributes.php b/src/XML/gssp/UserAttributes.php
new file mode 100644
index 000000000..0eaacf569
--- /dev/null
+++ b/src/XML/gssp/UserAttributes.php
@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\SAML2\XML\gssp;
+
+use Dom;
+use SimpleSAML\SAML2\Assert\Assert;
+use SimpleSAML\SAML2\XML\saml\Attribute;
+use SimpleSAML\XML\Constants as C;
+use SimpleSAML\XML\SchemaValidatableElementInterface;
+use SimpleSAML\XML\SchemaValidatableElementTrait;
+use SimpleSAML\XMLSchema\Exception\InvalidDOMElementException;
+use SimpleSAML\XMLSchema\Exception\MissingElementException;
+
+/**
+ * Class representing a GSSP UserAttributes-element
+ *
+ * @package simplesamlphp/saml2
+ */
+class UserAttributes extends AbstractGsspElement implements SchemaValidatableElementInterface
+{
+    use SchemaValidatableElementTrait;
+
+
+    /**
+     * UserAttributes constructor.
+     *
+     * @param \SimpleSAML\SAML2\XML\saml\Attribute[] $attributes
+     */
+    final public function __construct(
+        protected array $attributes = [],
+    ) {
+        Assert::minCount($attributes, 1, MissingElementException::class);
+        Assert::maxCount($attributes, C::UNBOUNDED_LIMIT);
+        Assert::allIsInstanceOf($attributes, Attribute::class);
+    }
+
+
+    /**
+     * @return \SimpleSAML\SAML2\XML\saml\Attribute[]
+     */
+    public function getAttributes(): array
+    {
+        return $this->attributes;
+    }
+
+
+    /**
+     * @throws \SimpleSAML\XMLSchema\Exception\InvalidDOMElementException
+     *   if the qualified name of the supplied element is wrong
+     */
+    public static function fromXML(Dom\Element $xml): static
+    {
+        Assert::same($xml->localName, 'UserAttributes', InvalidDOMElementException::class);
+        Assert::same($xml->namespaceURI, UserAttributes::NS, InvalidDOMElementException::class);
+
+        return new static(
+            Attribute::getChildrenOfClass($xml),
+        );
+    }
+
+
+    /**
+     * Convert this UserAttributes to XML.
+     */
+    public function toXML(?Dom\Element $parent = null): Dom\Element
+    {
+        $e = $this->instantiateParentElement($parent);
+
+        foreach ($this->getAttributes() as $attribute) {
+            $attribute->toXML($e);
+        }
+
+        return $e;
+    }
+}
diff --git a/tests/SAML2/XML/gssp/UserAttributesTest.php b/tests/SAML2/XML/gssp/UserAttributesTest.php
new file mode 100644
index 000000000..46db69d2b
--- /dev/null
+++ b/tests/SAML2/XML/gssp/UserAttributesTest.php
@@ -0,0 +1,106 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SimpleSAML\Test\SAML2\XML\gssp;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Group;
+use PHPUnit\Framework\TestCase;
+use SimpleSAML\SAML2\Constants as C;
+use SimpleSAML\SAML2\Type\SAMLAnyURIValue;
+use SimpleSAML\SAML2\Type\SAMLStringValue;
+use SimpleSAML\SAML2\XML\gssp\AbstractGsspElement;
+use SimpleSAML\SAML2\XML\gssp\UserAttributes;
+use SimpleSAML\SAML2\XML\saml\Attribute;
+use SimpleSAML\SAML2\XML\saml\AttributeValue;
+use SimpleSAML\XML\DOMDocumentFactory;
+use SimpleSAML\XML\TestUtils\SchemaValidationTestTrait;
+use SimpleSAML\XML\TestUtils\SerializableElementTestTrait;
+use SimpleSAML\XMLSchema\Exception\MissingElementException;
+
+use function dirname;
+use function strval;
+
+/**
+ * Class \SimpleSAML\SAML2\XML\gssp\UserAttributesTest
+ *
+ * @package simplesamlphp/saml2
+ */
+#[Group('gssp')]
+#[CoversClass(UserAttributes::class)]
+#[CoversClass(AbstractGsspElement::class)]
+final class UserAttributesTest extends TestCase
+{
+    use SchemaValidationTestTrait;
+    use SerializableElementTestTrait;
+
+
+    /**
+     */
+    public static function setUpBeforeClass(): void
+    {
+        self::$testedClass = UserAttributes::class;
+
+        self::$xmlRepresentation = DOMDocumentFactory::fromFile(
+            dirname(__FILE__, 4) . '/resources/xml/gssp_UserAttributes.xml',
+        );
+    }
+
+
+    // marshalling
+
+
+    /**
+     */
+    public function testMarshalling(): void
+    {
+        $userAttributes = new UserAttributes(
+            [
+                new Attribute(
+                    name: SAMLStringValue::fromString('urn:mace:dir:attribute-def:mail'),
+                    nameFormat: SAMLAnyURIValue::fromString(C::NAMEFORMAT_URI),
+                    attributeValue: [
+                        new AttributeValue(SAMLStringValue::fromString('user@example.com')),
+                    ],
+                ),
+            ],
+        );
+
+        $expectedXml = self::$xmlRepresentation->saveXml(self::$xmlRepresentation->documentElement);
+        $this->assertNotFalse($expectedXml);
+        $actualXml = strval($userAttributes);
+
+        $this->assertXmlStringEqualsXmlString($expectedXml, $actualXml);
+    }
+
+
+    /**
+     */
+    public function testMarshallingMissingAttributesThrowsException(): void
+    {
+        $this->expectException(MissingElementException::class);
+
+        new UserAttributes([]);
+    }
+
+
+    // unmarshalling
+
+
+    /**
+     */
+    public function testUnmarshallingMissingAttributesThrowsException(): void
+    {
+        $document = DOMDocumentFactory::fromString(
+            <<<XML
+<saml:UserAttributes xmlns:saml="urn:mace:surf.nl:stepup:gssp-extensions">
+</saml:UserAttributes>
+XML
+            ,
+        );
+
+        $this->expectException(MissingElementException::class);
+        UserAttributes::fromXML($document->documentElement);
+    }
+}
diff --git a/tests/SAML2/XML/samlp/AuthnRequestTest.php b/tests/SAML2/XML/samlp/AuthnRequestTest.php
index 059ac86c1..f4ac515a5 100644
--- a/tests/SAML2/XML/samlp/AuthnRequestTest.php
+++ b/tests/SAML2/XML/samlp/AuthnRequestTest.php
@@ -17,7 +17,9 @@
 use SimpleSAML\SAML2\Type\SAMLStringValue;
 use SimpleSAML\SAML2\Utils;
 use SimpleSAML\SAML2\Utils\XPath;
-use SimpleSAML\SAML2\XML\aslo\Asynchronous;
+use SimpleSAML\SAML2\XML\gssp\UserAttributes;
+use SimpleSAML\SAML2\XML\saml\Attribute;
+use SimpleSAML\SAML2\XML\saml\AttributeValue;
 use SimpleSAML\SAML2\XML\saml\Audience;
 use SimpleSAML\SAML2\XML\saml\AudienceRestriction;
 use SimpleSAML\SAML2\XML\saml\AuthnContextClassRef;
@@ -104,8 +106,15 @@ public function testMarshalling(): void
         );
 
         $extensions = new Extensions([
-            // Note:  this makes zero sense in an AuthnRequest, but we can't be picky in what extensions we accept
-            new Asynchronous(),
+            new UserAttributes([
+                new Attribute(
+                    name: SAMLStringValue::fromString('urn:mace:dir:attribute-def:mail'),
+                    nameFormat: SAMLAnyURIValue::fromString(C::NAMEFORMAT_URI),
+                    attributeValue: [
+                        new AttributeValue(SAMLStringValue::fromString('user@example.com')),
+                    ],
+                ),
+            ]),
         ]);
 
         $authnRequest = new AuthnRequest(
@@ -191,8 +200,15 @@ public function testMarshallingElementOrdering(): void
 
         // Create Extensions
         $extensions = new Extensions([
-            // Note:  this makes zero sense in an AuthnRequest, but we can't be picky in what extensions we accept
-            new Asynchronous(),
+            new UserAttributes([
+                new Attribute(
+                    name: SAMLStringValue::fromString('urn:mace:dir:attribute-def:mail'),
+                    nameFormat: SAMLAnyURIValue::fromString(C::NAMEFORMAT_URI),
+                    attributeValue: [
+                        new AttributeValue(SAMLStringValue::fromString('user@example.com')),
+                    ],
+                ),
+            ]),
         ]);
 
         $authnRequest = new AuthnRequest(
diff --git a/tests/resources/xml/gssp_UserAttributes.xml b/tests/resources/xml/gssp_UserAttributes.xml
new file mode 100644
index 000000000..cbf1f5abf
--- /dev/null
+++ b/tests/resources/xml/gssp_UserAttributes.xml
@@ -0,0 +1,5 @@
+<gssp:UserAttributes xmlns:gssp="urn:mace:surf.nl:stepup:gssp-extensions" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">
+  <saml:Attribute Name="urn:mace:dir:attribute-def:mail" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri">
+    <saml:AttributeValue>user@example.com</saml:AttributeValue>
+  </saml:Attribute>
+</gssp:UserAttributes>
diff --git a/tests/resources/xml/samlp_AuthnRequest.xml b/tests/resources/xml/samlp_AuthnRequest.xml
index 6d8970f4c..3faa60ccd 100644
--- a/tests/resources/xml/samlp_AuthnRequest.xml
+++ b/tests/resources/xml/samlp_AuthnRequest.xml
@@ -1,7 +1,11 @@
-<samlp:AuthnRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" xmlns:aslo="urn:oasis:names:tc:SAML:2.0:protocol:ext:async-slo" Version="2.0" ID="_2b0226190ca1c22de6f66e85f5c95158" IssueInstant="2014-09-22T13:42:00Z" Destination="https://tiqr.stepup.org/idp/profile/saml2/Redirect/SSO" Consent="urn:oasis:names:tc:SAML:2.0:consent:unspecified">
+<samlp:AuthnRequest xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" xmlns:gssp="urn:mace:surf.nl:stepup:gssp-extensions" Version="2.0" ID="_2b0226190ca1c22de6f66e85f5c95158" IssueInstant="2014-09-22T13:42:00Z" Destination="https://tiqr.stepup.org/idp/profile/saml2/Redirect/SSO" Consent="urn:oasis:names:tc:SAML:2.0:consent:unspecified">
   <saml:Issuer>https://gateway.stepup.org/saml20/sp/metadata</saml:Issuer>
   <samlp:Extensions>
-    <aslo:Asynchronous/>
+    <gssp:UserAttributes>
+      <saml:Attribute Name="urn:mace:dir:attribute-def:mail" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri">
+        <saml:AttributeValue>user@example.com</saml:AttributeValue>
+      </saml:Attribute>
+    </gssp:UserAttributes>
   </samlp:Extensions>
   <saml:Subject>
     <saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified">user@example.org</saml:NameID>