diff --git a/crates/caldav/src/principal/mod.rs b/crates/caldav/src/principal/mod.rs
index e4f248d..11a5e9c 100644
--- a/crates/caldav/src/principal/mod.rs
+++ b/crates/caldav/src/principal/mod.rs
@@ -63,6 +63,15 @@ impl Resource for PrincipalResource {
                     PrincipalPropName::CalendarUserAddressSet => {
                         PrincipalProp::CalendarUserAddressSet(principal_url.into())
                     }
+                    PrincipalPropName::GroupMembership => {
+                        PrincipalProp::GroupMembership(GroupMembership(
+                            user.memberships_without_self()
+                                .iter()
+                                .map(|principal| puri.principal_uri(principal).into())
+                                .collect(),
+                        ))
+                    }
+                    PrincipalPropName::AlternateUriSet => PrincipalProp::AlternateUriSet,
                 })
             }
             PrincipalPropWrapperName::Common(prop) => PrincipalPropWrapper::Common(
diff --git a/crates/caldav/src/principal/prop.rs b/crates/caldav/src/principal/prop.rs
index 2cb4fb5..fa3043a 100644
--- a/crates/caldav/src/principal/prop.rs
+++ b/crates/caldav/src/principal/prop.rs
@@ -14,6 +14,10 @@ pub enum PrincipalProp {
     // WebDAV Access Control (RFC 3744)
     #[xml(ns = "rustical_dav::namespace::NS_DAV", rename = b"principal-URL")]
     PrincipalUrl(HrefElement),
+    #[xml(ns = "rustical_dav::namespace::NS_DAV")]
+    GroupMembership(GroupMembership),
+    #[xml(ns = "rustical_dav::namespace::NS_DAV", rename = b"alternate-URI-set")]
+    AlternateUriSet,
 
     // CalDAV (RFC 4791)
     #[xml(ns = "rustical_dav::namespace::NS_CALDAV")]
@@ -29,3 +33,6 @@ pub enum PrincipalPropWrapper {
 
 #[derive(XmlDeserialize, XmlSerialize, PartialEq, Clone)]
 pub struct CalendarHomeSet(#[xml(ty = "untagged", flatten)] pub(super) Vec<HrefElement>);
+
+#[derive(XmlDeserialize, XmlSerialize, PartialEq, Clone)]
+pub struct GroupMembership(#[xml(ty = "untagged", flatten)] pub(super) Vec<HrefElement>);
diff --git a/crates/carddav/src/principal/mod.rs b/crates/carddav/src/principal/mod.rs
index 5bb0bc9..a7186ff 100644
--- a/crates/carddav/src/principal/mod.rs
+++ b/crates/carddav/src/principal/mod.rs
@@ -59,6 +59,15 @@ impl Resource for PrincipalResource {
                         PrincipalProp::AddressbookHomeSet(home_set)
                     }
                     PrincipalPropName::PrincipalAddress => PrincipalProp::PrincipalAddress(None),
+                    PrincipalPropName::GroupMembership => {
+                        PrincipalProp::GroupMembership(GroupMembership(
+                            user.memberships_without_self()
+                                .iter()
+                                .map(|principal| puri.principal_uri(principal).into())
+                                .collect(),
+                        ))
+                    }
+                    PrincipalPropName::AlternateUriSet => PrincipalProp::AlternateUriSet,
                 })
             }
 
diff --git a/crates/carddav/src/principal/prop.rs b/crates/carddav/src/principal/prop.rs
index e749e1f..3a6d968 100644
--- a/crates/carddav/src/principal/prop.rs
+++ b/crates/carddav/src/principal/prop.rs
@@ -11,6 +11,10 @@ pub enum PrincipalProp {
     #[xml(rename = b"principal-URL")]
     #[xml(ns = "rustical_dav::namespace::NS_DAV")]
     PrincipalUrl(HrefElement),
+    #[xml(ns = "rustical_dav::namespace::NS_DAV")]
+    GroupMembership(GroupMembership),
+    #[xml(ns = "rustical_dav::namespace::NS_DAV", rename = b"alternate-URI-set")]
+    AlternateUriSet,
 
     // CardDAV (RFC 6352)
     #[xml(ns = "rustical_dav::namespace::NS_CARDDAV")]
@@ -25,3 +29,6 @@ pub enum PrincipalPropWrapper {
     Principal(PrincipalProp),
     Common(CommonPropertiesProp),
 }
+
+#[derive(XmlDeserialize, XmlSerialize, PartialEq, Clone)]
+pub struct GroupMembership(#[xml(ty = "untagged", flatten)] pub(super) Vec<HrefElement>);
diff --git a/crates/store/src/auth/user.rs b/crates/store/src/auth/user.rs
index e7710a8..284cc23 100644
--- a/crates/store/src/auth/user.rs
+++ b/crates/store/src/auth/user.rs
@@ -108,6 +108,10 @@ impl User {
         memberships.push(self.id.as_str());
         memberships
     }
+
+    pub fn memberships_without_self(&self) -> Vec<&str> {
+        self.memberships.iter().map(String::as_str).collect()
+    }
 }
 
 impl rustical_dav::Principal for User {