Resolve user to stable unique ID in policy (#2205)

hscontrol/app.go

@@ -1029,14 +1029,18 @@ func (h *Headscale) loadACLPolicy() error {
 		if err != nil {
 			return fmt.Errorf("loading nodes from database to validate policy: %w", err)
 		}
+		users, err := h.db.ListUsers()
+		if err != nil {
+			return fmt.Errorf("loading users from database to validate policy: %w", err)
+		}
 
-		_, err = pol.CompileFilterRules(nodes)
+		_, err = pol.CompileFilterRules(users, nodes)
 		if err != nil {
 			return fmt.Errorf("verifying policy rules: %w", err)
 		}
 
 		if len(nodes) > 0 {
-			_, err = pol.CompileSSHPolicy(nodes[0], nodes)
+			_, err = pol.CompileSSHPolicy(nodes[0], users, nodes)
 			if err != nil {
 				return fmt.Errorf("verifying SSH rules: %w", err)
 			}

hscontrol/db/node_test.go

@@ -256,10 +256,10 @@ func (s *Suite) TestGetACLFilteredPeers(c *check.C) {
 	c.Assert(err, check.IsNil)
 	c.Assert(len(testPeers), check.Equals, 9)
 
-	adminRules, _, err := policy.GenerateFilterAndSSHRulesForTests(aclPolicy, adminNode, adminPeers)
+	adminRules, _, err := policy.GenerateFilterAndSSHRulesForTests(aclPolicy, adminNode, adminPeers, []types.User{*stor[0].user, *stor[1].user})
 	c.Assert(err, check.IsNil)
 
-	testRules, _, err := policy.GenerateFilterAndSSHRulesForTests(aclPolicy, testNode, testPeers)
+	testRules, _, err := policy.GenerateFilterAndSSHRulesForTests(aclPolicy, testNode, testPeers, []types.User{*stor[0].user, *stor[1].user})
 	c.Assert(err, check.IsNil)
 
 	peersOfAdminNode := policy.FilterNodesByACL(adminNode, adminPeers, adminRules)

hscontrol/db/routes.go

@@ -648,8 +648,13 @@ func EnableAutoApprovedRoutes(
 			if approvedAlias == node.User.Username() {
 				approvedRoutes = append(approvedRoutes, advertisedRoute)
 			} else {
+				users, err := ListUsers(tx)
+				if err != nil {
+					return fmt.Errorf("looking up users to expand route alias: %w", err)
+				}
+
 				// TODO(kradalby): figure out how to get this to depend on less stuff
-				approvedIps, err := aclPolicy.ExpandAlias(types.Nodes{node}, approvedAlias)
+				approvedIps, err := aclPolicy.ExpandAlias(types.Nodes{node}, users, approvedAlias)
 				if err != nil {
 					return fmt.Errorf("expanding alias %q for autoApprovers: %w", approvedAlias, err)
 				}

hscontrol/grpcv1.go

@@ -773,14 +773,18 @@ func (api headscaleV1APIServer) SetPolicy(
 	if err != nil {
 		return nil, fmt.Errorf("loading nodes from database to validate policy: %w", err)
 	}
+	users, err := api.h.db.ListUsers()
+	if err != nil {
+		return nil, fmt.Errorf("loading users from database to validate policy: %w", err)
+	}
 
-	_, err = pol.CompileFilterRules(nodes)
+	_, err = pol.CompileFilterRules(users, nodes)
 	if err != nil {
 		return nil, fmt.Errorf("verifying policy rules: %w", err)
 	}
 
 	if len(nodes) > 0 {
-		_, err = pol.CompileSSHPolicy(nodes[0], nodes)
+		_, err = pol.CompileSSHPolicy(nodes[0], users, nodes)
 		if err != nil {
 			return nil, fmt.Errorf("verifying SSH rules: %w", err)
 		}

hscontrol/mapper/mapper.go

@@ -153,6 +153,7 @@ func addNextDNSMetadata(resolvers []*dnstype.Resolver, node *types.Node) {
 func (m *Mapper) fullMapResponse(
 	node *types.Node,
 	peers types.Nodes,
+	users []types.User,
 	pol *policy.ACLPolicy,
 	capVer tailcfg.CapabilityVersion,
 ) (*tailcfg.MapResponse, error) {
@@ -167,6 +168,7 @@ func (m *Mapper) fullMapResponse(
 		pol,
 		node,
 		capVer,
+		users,
 		peers,
 		peers,
 		m.cfg,
@@ -189,8 +191,12 @@ func (m *Mapper) FullMapResponse(
 	if err != nil {
 		return nil, err
 	}
+	users, err := m.db.ListUsers()
+	if err != nil {
+		return nil, err
+	}
 
-	resp, err := m.fullMapResponse(node, peers, pol, mapRequest.Version)
+	resp, err := m.fullMapResponse(node, peers, users, pol, mapRequest.Version)
 	if err != nil {
 		return nil, err
 	}
@@ -253,6 +259,11 @@ func (m *Mapper) PeerChangedResponse(
 		return nil, err
 	}
 
+	users, err := m.db.ListUsers()
+	if err != nil {
+		return nil, fmt.Errorf("listing users for map response: %w", err)
+	}
+
 	var removedIDs []tailcfg.NodeID
 	var changedIDs []types.NodeID
 	for nodeID, nodeChanged := range changed {
@@ -276,6 +287,7 @@ func (m *Mapper) PeerChangedResponse(
 		pol,
 		node,
 		mapRequest.Version,
+		users,
 		peers,
 		changedNodes,
 		m.cfg,
@@ -508,16 +520,17 @@ func appendPeerChanges(
 	pol *policy.ACLPolicy,
 	node *types.Node,
 	capVer tailcfg.CapabilityVersion,
+	users []types.User,
 	peers types.Nodes,
 	changed types.Nodes,
 	cfg *types.Config,
 ) error {
-	packetFilter, err := pol.CompileFilterRules(append(peers, node))
+	packetFilter, err := pol.CompileFilterRules(users, append(peers, node))
 	if err != nil {
 		return err
 	}
 
-	sshPolicy, err := pol.CompileSSHPolicy(node, peers)
+	sshPolicy, err := pol.CompileSSHPolicy(node, users, peers)
 	if err != nil {
 		return err
 	}

hscontrol/mapper/mapper_test.go

@@ -159,6 +159,9 @@ func Test_fullMapResponse(t *testing.T) {
 	lastSeen := time.Date(2009, time.November, 10, 23, 9, 0, 0, time.UTC)
 	expire := time.Date(2500, time.November, 11, 23, 0, 0, 0, time.UTC)
 
+	user1 := types.User{Model: gorm.Model{ID: 0}, Name: "mini"}
+	user2 := types.User{Model: gorm.Model{ID: 1}, Name: "peer2"}
+
 	mini := &types.Node{
 		ID: 0,
 		MachineKey: mustMK(
@@ -173,8 +176,8 @@ func Test_fullMapResponse(t *testing.T) {
 		IPv4:       iap("100.64.0.1"),
 		Hostname:   "mini",
 		GivenName:  "mini",
-		UserID:     0,
+		UserID:     user1.ID,
-		User:       types.User{Name: "mini"},
+		User:       user1,
 		ForcedTags: []string{},
 		AuthKey:    &types.PreAuthKey{},
 		LastSeen:   &lastSeen,
@@ -253,8 +256,8 @@ func Test_fullMapResponse(t *testing.T) {
 		IPv4:       iap("100.64.0.2"),
 		Hostname:   "peer1",
 		GivenName:  "peer1",
-		UserID:     0,
+		UserID:     user1.ID,
-		User:       types.User{Name: "mini"},
+		User:       user1,
 		ForcedTags: []string{},
 		LastSeen:   &lastSeen,
 		Expiry:     &expire,
@@ -308,8 +311,8 @@ func Test_fullMapResponse(t *testing.T) {
 		IPv4:       iap("100.64.0.3"),
 		Hostname:   "peer2",
 		GivenName:  "peer2",
-		UserID:     1,
+		UserID:     user2.ID,
-		User:       types.User{Name: "peer2"},
+		User:       user2,
 		ForcedTags: []string{},
 		LastSeen:   &lastSeen,
 		Expiry:     &expire,
@@ -468,6 +471,7 @@ func Test_fullMapResponse(t *testing.T) {
 			got, err := mappy.fullMapResponse(
 				tt.node,
 				tt.peers,
+				[]types.User{user1, user2},
 				tt.pol,
 				0,
 			)

hscontrol/policy/acls.go

@@ -137,20 +137,21 @@ func GenerateFilterAndSSHRulesForTests(
 	policy *ACLPolicy,
 	node *types.Node,
 	peers types.Nodes,
+	users []types.User,
 ) ([]tailcfg.FilterRule, *tailcfg.SSHPolicy, error) {
 	// If there is no policy defined, we default to allow all
 	if policy == nil {
 		return tailcfg.FilterAllowAll, &tailcfg.SSHPolicy{}, nil
 	}
 
-	rules, err := policy.CompileFilterRules(append(peers, node))
+	rules, err := policy.CompileFilterRules(users, append(peers, node))
 	if err != nil {
 		return []tailcfg.FilterRule{}, &tailcfg.SSHPolicy{}, err
 	}
 
 	log.Trace().Interface("ACL", rules).Str("node", node.GivenName).Msg("ACL rules")
 
-	sshPolicy, err := policy.CompileSSHPolicy(node, peers)
+	sshPolicy, err := policy.CompileSSHPolicy(node, users, peers)
 	if err != nil {
 		return []tailcfg.FilterRule{}, &tailcfg.SSHPolicy{}, err
 	}
@@ -161,6 +162,7 @@ func GenerateFilterAndSSHRulesForTests(
 // CompileFilterRules takes a set of nodes and an ACLPolicy and generates a
 // set of Tailscale compatible FilterRules used to allow traffic on clients.
 func (pol *ACLPolicy) CompileFilterRules(
+	users []types.User,
 	nodes types.Nodes,
 ) ([]tailcfg.FilterRule, error) {
 	if pol == nil {
@@ -176,7 +178,7 @@ func (pol *ACLPolicy) CompileFilterRules(
 
 		var srcIPs []string
 		for srcIndex, src := range acl.Sources {
-			srcs, err := pol.expandSource(src, nodes)
+			srcs, err := pol.expandSource(src, users, nodes)
 			if err != nil {
 				return nil, fmt.Errorf(
 					"parsing policy, acl index: %d->%d: %w",
@@ -202,6 +204,7 @@ func (pol *ACLPolicy) CompileFilterRules(
 
 			expanded, err := pol.ExpandAlias(
 				nodes,
+				users,
 				alias,
 			)
 			if err != nil {
@@ -286,6 +289,7 @@ func ReduceFilterRules(node *types.Node, rules []tailcfg.FilterRule) []tailcfg.F
 
 func (pol *ACLPolicy) CompileSSHPolicy(
 	node *types.Node,
+	users []types.User,
 	peers types.Nodes,
 ) (*tailcfg.SSHPolicy, error) {
 	if pol == nil {
@@ -317,7 +321,7 @@ func (pol *ACLPolicy) CompileSSHPolicy(
 	for index, sshACL := range pol.SSHs {
 		var dest netipx.IPSetBuilder
 		for _, src := range sshACL.Destinations {
-			expanded, err := pol.ExpandAlias(append(peers, node), src)
+			expanded, err := pol.ExpandAlias(append(peers, node), users, src)
 			if err != nil {
 				return nil, err
 			}
@@ -377,6 +381,7 @@ func (pol *ACLPolicy) CompileSSHPolicy(
 			} else {
 				expandedSrcs, err := pol.ExpandAlias(
 					peers,
+					users,
 					rawSrc,
 				)
 				if err != nil {
@@ -526,9 +531,10 @@ func parseProtocol(protocol string) ([]int, bool, error) {
 // with the given src alias.
 func (pol *ACLPolicy) expandSource(
 	src string,
+	users []types.User,
 	nodes types.Nodes,
 ) ([]string, error) {
-	ipSet, err := pol.ExpandAlias(nodes, src)
+	ipSet, err := pol.ExpandAlias(nodes, users, src)
 	if err != nil {
 		return []string{}, err
 	}
@@ -552,6 +558,7 @@ func (pol *ACLPolicy) expandSource(
 // and transform these in IPAddresses.
 func (pol *ACLPolicy) ExpandAlias(
 	nodes types.Nodes,
+	users []types.User,
 	alias string,
 ) (*netipx.IPSet, error) {
 	if isWildcard(alias) {
@@ -566,12 +573,12 @@ func (pol *ACLPolicy) ExpandAlias(
 
 	// if alias is a group
 	if isGroup(alias) {
-		return pol.expandIPsFromGroup(alias, nodes)
+		return pol.expandIPsFromGroup(alias, users, nodes)
 	}
 
 	// if alias is a tag
 	if isTag(alias) {
-		return pol.expandIPsFromTag(alias, nodes)
+		return pol.expandIPsFromTag(alias, users, nodes)
 	}
 
 	if isAutoGroup(alias) {
@@ -579,7 +586,7 @@ func (pol *ACLPolicy) ExpandAlias(
 	}
 
 	// if alias is a user
-	if ips, err := pol.expandIPsFromUser(alias, nodes); ips != nil {
+	if ips, err := pol.expandIPsFromUser(alias, users, nodes); ips != nil {
 		return ips, err
 	}
 
@@ -588,7 +595,7 @@ func (pol *ACLPolicy) ExpandAlias(
 	if h, ok := pol.Hosts[alias]; ok {
 		log.Trace().Str("host", h.String()).Msg("ExpandAlias got hosts entry")
 
-		return pol.ExpandAlias(nodes, h.String())
+		return pol.ExpandAlias(nodes, users, h.String())
 	}
 
 	// if alias is an IP
@@ -765,16 +772,17 @@ func (pol *ACLPolicy) expandUsersFromGroup(
 
 func (pol *ACLPolicy) expandIPsFromGroup(
 	group string,
+	users []types.User,
 	nodes types.Nodes,
 ) (*netipx.IPSet, error) {
 	var build netipx.IPSetBuilder
 
-	users, err := pol.expandUsersFromGroup(group)
+	userTokens, err := pol.expandUsersFromGroup(group)
 	if err != nil {
 		return &netipx.IPSet{}, err
 	}
-	for _, user := range users {
+	for _, user := range userTokens {
-		filteredNodes := filterNodesByUser(nodes, user)
+		filteredNodes := filterNodesByUser(nodes, users, user)
 		for _, node := range filteredNodes {
 			node.AppendToIPSet(&build)
 		}
@@ -785,6 +793,7 @@ func (pol *ACLPolicy) expandIPsFromGroup(
 
 func (pol *ACLPolicy) expandIPsFromTag(
 	alias string,
+	users []types.User,
 	nodes types.Nodes,
 ) (*netipx.IPSet, error) {
 	var build netipx.IPSetBuilder
@@ -817,7 +826,7 @@ func (pol *ACLPolicy) expandIPsFromTag(
 
 	// filter out nodes per tag owner
 	for _, user := range owners {
-		nodes := filterNodesByUser(nodes, user)
+		nodes := filterNodesByUser(nodes, users, user)
 		for _, node := range nodes {
 			if node.Hostinfo == nil {
 				continue
@@ -834,11 +843,12 @@ func (pol *ACLPolicy) expandIPsFromTag(
 
 func (pol *ACLPolicy) expandIPsFromUser(
 	user string,
+	users []types.User,
 	nodes types.Nodes,
 ) (*netipx.IPSet, error) {
 	var build netipx.IPSetBuilder
 
-	filteredNodes := filterNodesByUser(nodes, user)
+	filteredNodes := filterNodesByUser(nodes, users, user)
 	filteredNodes = excludeCorrectlyTaggedNodes(pol, filteredNodes, user)
 
 	// shortcurcuit if we have no nodes to get ips from.
@@ -967,10 +977,43 @@ func (pol *ACLPolicy) TagsOfNode(
 	return validTags, invalidTags
 }
 
-func filterNodesByUser(nodes types.Nodes, user string) types.Nodes {
+// filterNodesByUser returns a list of nodes that match the given userToken from a
+// policy.
+// Matching nodes are determined by first matching the user token to a user by checking:
+// - If it is an ID that mactches the user database ID
+// - It is the Provider Identifier from OIDC
+// - It matches the username or email of a user
+//
+// If the token matches more than one user, zero nodes will returned.
+func filterNodesByUser(nodes types.Nodes, users []types.User, userToken string) types.Nodes {
 	var out types.Nodes
+
+	var potentialUsers []types.User
+	for _, user := range users {
+		if user.ProviderIdentifier.Valid && user.ProviderIdentifier.String == userToken {
+			// If a user is matching with a known unique field,
+			// disgard all other users and only keep the current
+			// user.
+			potentialUsers = []types.User{user}
+
+			break
+		}
+		if user.Email == userToken {
+			potentialUsers = append(potentialUsers, user)
+		}
+		if user.Name == userToken {
+			potentialUsers = append(potentialUsers, user)
+		}
+	}
+
+	if len(potentialUsers) != 1 {
+		return nil
+	}
+
+	user := potentialUsers[0]
+
 	for _, node := range nodes {
-		if node.User.Username() == user {
+		if node.User.ID == user.ID {
 			out = append(out, node)
 		}
 	}

hscontrol/policy/acls_test.go

@@ -1,9 +1,12 @@
 package policy
 
 import (
+	"database/sql"
 	"errors"
+	"math/rand/v2"
 	"net/netip"
 	"slices"
+	"sort"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -14,6 +17,7 @@ import (
 	"github.com/stretchr/testify/require"
 	"go4.org/netipx"
 	"gopkg.in/check.v1"
+	"gorm.io/gorm"
 	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 )
@@ -375,15 +379,21 @@ func TestParsing(t *testing.T) {
 				return
 			}
 
-			rules, err := pol.CompileFilterRules(types.Nodes{
+			user := types.User{
+				Model: gorm.Model{ID: 1},
+				Name:  "testuser",
+			}
+			rules, err := pol.CompileFilterRules(
+				[]types.User{
+					user,
+				},
+				types.Nodes{
 					&types.Node{
 						IPv4: iap("100.100.100.100"),
 					},
 					&types.Node{
 						IPv4:     iap("200.200.200.200"),
-					User: types.User{
+						User:     user,
-						Name: "testuser",
-					},
 						Hostinfo: &tailcfg.Hostinfo{},
 					},
 				})
@@ -533,7 +543,7 @@ func (s *Suite) TestRuleInvalidGeneration(c *check.C) {
 	c.Assert(pol.ACLs, check.HasLen, 6)
 	c.Assert(err, check.IsNil)
 
-	rules, err := pol.CompileFilterRules(types.Nodes{})
+	rules, err := pol.CompileFilterRules([]types.User{}, types.Nodes{})
 	c.Assert(err, check.NotNil)
 	c.Assert(rules, check.IsNil)
 }
@@ -549,7 +559,12 @@ func (s *Suite) TestInvalidAction(c *check.C) {
 			},
 		},
 	}
-	_, _, err := GenerateFilterAndSSHRulesForTests(pol, &types.Node{}, types.Nodes{})
+	_, _, err := GenerateFilterAndSSHRulesForTests(
+		pol,
+		&types.Node{},
+		types.Nodes{},
+		[]types.User{},
+	)
 	c.Assert(errors.Is(err, ErrInvalidAction), check.Equals, true)
 }
 
@@ -568,7 +583,12 @@ func (s *Suite) TestInvalidGroupInGroup(c *check.C) {
 			},
 		},
 	}
-	_, _, err := GenerateFilterAndSSHRulesForTests(pol, &types.Node{}, types.Nodes{})
+	_, _, err := GenerateFilterAndSSHRulesForTests(
+		pol,
+		&types.Node{},
+		types.Nodes{},
+		[]types.User{},
+	)
 	c.Assert(errors.Is(err, ErrInvalidGroup), check.Equals, true)
 }
 
@@ -584,7 +604,12 @@ func (s *Suite) TestInvalidTagOwners(c *check.C) {
 		},
 	}
 
-	_, _, err := GenerateFilterAndSSHRulesForTests(pol, &types.Node{}, types.Nodes{})
+	_, _, err := GenerateFilterAndSSHRulesForTests(
+		pol,
+		&types.Node{},
+		types.Nodes{},
+		[]types.User{},
+	)
 	c.Assert(errors.Is(err, ErrInvalidTag), check.Equals, true)
 }
 
@@ -860,7 +885,25 @@ func Test_expandPorts(t *testing.T) {
 	}
 }
 
-func Test_listNodesInUser(t *testing.T) {
+func Test_filterNodesByUser(t *testing.T) {
+	users := []types.User{
+		{Model: gorm.Model{ID: 1}, Name: "marc"},
+		{Model: gorm.Model{ID: 2}, Name: "joe", Email: "joe@headscale.net"},
+		{
+			Model:              gorm.Model{ID: 3},
+			Name:               "mikael",
+			Email:              "mikael@headscale.net",
+			ProviderIdentifier: sql.NullString{String: "http://oidc.org/1234", Valid: true},
+		},
+		{Model: gorm.Model{ID: 4}, Name: "mikael2", Email: "mikael@headscale.net"},
+		{Model: gorm.Model{ID: 5}, Name: "mikael", Email: "mikael2@headscale.net"},
+		{Model: gorm.Model{ID: 6}, Name: "http://oidc.org/1234", Email: "mikael@headscale.net"},
+		{Model: gorm.Model{ID: 7}, Name: "1"},
+		{Model: gorm.Model{ID: 8}, Name: "alex", Email: "alex@headscale.net"},
+		{Model: gorm.Model{ID: 9}, Name: "alex@headscale.net"},
+		{Model: gorm.Model{ID: 10}, Email: "http://oidc.org/1234"},
+	}
+
 	type args struct {
 		nodes types.Nodes
 		user  string
@@ -874,50 +917,258 @@ func Test_listNodesInUser(t *testing.T) {
 			name: "1 node in user",
 			args: args{
 				nodes: types.Nodes{
-					&types.Node{User: types.User{Name: "joe"}},
+					&types.Node{User: users[1]},
 				},
 				user: "joe",
 			},
 			want: types.Nodes{
-				&types.Node{User: types.User{Name: "joe"}},
+				&types.Node{User: users[1]},
 			},
 		},
 		{
 			name: "3 nodes, 2 in user",
 			args: args{
 				nodes: types.Nodes{
-					&types.Node{ID: 1, User: types.User{Name: "joe"}},
+					&types.Node{ID: 1, User: users[1]},
-					&types.Node{ID: 2, User: types.User{Name: "marc"}},
+					&types.Node{ID: 2, User: users[0]},
-					&types.Node{ID: 3, User: types.User{Name: "marc"}},
+					&types.Node{ID: 3, User: users[0]},
 				},
 				user: "marc",
 			},
 			want: types.Nodes{
-				&types.Node{ID: 2, User: types.User{Name: "marc"}},
+				&types.Node{ID: 2, User: users[0]},
-				&types.Node{ID: 3, User: types.User{Name: "marc"}},
+				&types.Node{ID: 3, User: users[0]},
 			},
 		},
 		{
 			name: "5 nodes, 0 in user",
 			args: args{
 				nodes: types.Nodes{
-					&types.Node{ID: 1, User: types.User{Name: "joe"}},
+					&types.Node{ID: 1, User: users[1]},
-					&types.Node{ID: 2, User: types.User{Name: "marc"}},
+					&types.Node{ID: 2, User: users[0]},
-					&types.Node{ID: 3, User: types.User{Name: "marc"}},
+					&types.Node{ID: 3, User: users[0]},
-					&types.Node{ID: 4, User: types.User{Name: "marc"}},
+					&types.Node{ID: 4, User: users[0]},
-					&types.Node{ID: 5, User: types.User{Name: "marc"}},
+					&types.Node{ID: 5, User: users[0]},
 				},
 				user: "mickael",
 			},
 			want: nil,
 		},
+		{
+			name: "match-by-provider-ident",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[1]},
+					&types.Node{ID: 2, User: users[2]},
+				},
+				user: "http://oidc.org/1234",
+			},
+			want: types.Nodes{
+				&types.Node{ID: 2, User: users[2]},
+			},
+		},
+		{
+			name: "match-by-email",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[1]},
+					&types.Node{ID: 2, User: users[2]},
+					&types.Node{ID: 8, User: users[7]},
+				},
+				user: "joe@headscale.net",
+			},
+			want: types.Nodes{
+				&types.Node{ID: 1, User: users[1]},
+			},
+		},
+		{
+			name: "multi-match-is-zero",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[1]},
+					&types.Node{ID: 2, User: users[2]},
+					&types.Node{ID: 3, User: users[3]},
+				},
+				user: "mikael@headscale.net",
+			},
+			want: nil,
+		},
+		{
+			name: "multi-email-first-match-is-zero",
+			args: args{
+				nodes: types.Nodes{
+					// First match email, then provider id
+					&types.Node{ID: 3, User: users[3]},
+					&types.Node{ID: 2, User: users[2]},
+				},
+				user: "mikael@headscale.net",
+			},
+			want: nil,
+		},
+		{
+			name: "multi-username-first-match-is-zero",
+			args: args{
+				nodes: types.Nodes{
+					// First match username, then provider id
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 2, User: users[2]},
+				},
+				user: "mikael",
+			},
+			want: nil,
+		},
+		{
+			name: "all-users-duplicate-username-random-order",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[0]},
+					&types.Node{ID: 2, User: users[1]},
+					&types.Node{ID: 3, User: users[2]},
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 5, User: users[4]},
+				},
+				user: "mikael",
+			},
+			want: nil,
+		},
+		{
+			name: "all-users-unique-username-random-order",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[0]},
+					&types.Node{ID: 2, User: users[1]},
+					&types.Node{ID: 3, User: users[2]},
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 5, User: users[4]},
+				},
+				user: "marc",
+			},
+			want: types.Nodes{
+				&types.Node{ID: 1, User: users[0]},
+			},
+		},
+		{
+			name: "all-users-no-username-random-order",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[0]},
+					&types.Node{ID: 2, User: users[1]},
+					&types.Node{ID: 3, User: users[2]},
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 5, User: users[4]},
+				},
+				user: "not-working",
+			},
+			want: nil,
+		},
+		{
+			name: "all-users-duplicate-email-random-order",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[0]},
+					&types.Node{ID: 2, User: users[1]},
+					&types.Node{ID: 3, User: users[2]},
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 5, User: users[4]},
+				},
+				user: "mikael@headscale.net",
+			},
+			want: nil,
+		},
+		{
+			name: "all-users-duplicate-email-random-order",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[0]},
+					&types.Node{ID: 2, User: users[1]},
+					&types.Node{ID: 3, User: users[2]},
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 5, User: users[4]},
+					&types.Node{ID: 8, User: users[7]},
+				},
+				user: "joe@headscale.net",
+			},
+			want: types.Nodes{
+				&types.Node{ID: 2, User: users[1]},
+			},
+		},
+		{
+			name: "email-as-username-duplicate",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[7]},
+					&types.Node{ID: 2, User: users[8]},
+				},
+				user: "alex@headscale.net",
+			},
+			want: nil,
+		},
+		{
+			name: "all-users-no-email-random-order",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[0]},
+					&types.Node{ID: 2, User: users[1]},
+					&types.Node{ID: 3, User: users[2]},
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 5, User: users[4]},
+				},
+				user: "not-working@headscale.net",
+			},
+			want: nil,
+		},
+		{
+			name: "all-users-provider-id-random-order",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[0]},
+					&types.Node{ID: 2, User: users[1]},
+					&types.Node{ID: 3, User: users[2]},
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 5, User: users[4]},
+					&types.Node{ID: 6, User: users[5]},
+				},
+				user: "http://oidc.org/1234",
+			},
+			want: types.Nodes{
+				&types.Node{ID: 3, User: users[2]},
+			},
+		},
+		{
+			name: "all-users-no-provider-id-random-order",
+			args: args{
+				nodes: types.Nodes{
+					&types.Node{ID: 1, User: users[0]},
+					&types.Node{ID: 2, User: users[1]},
+					&types.Node{ID: 3, User: users[2]},
+					&types.Node{ID: 4, User: users[3]},
+					&types.Node{ID: 5, User: users[4]},
+					&types.Node{ID: 6, User: users[5]},
+				},
+				user: "http://oidc.org/4321",
+			},
+			want: nil,
+		},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			got := filterNodesByUser(test.args.nodes, test.args.user)
+			for range 1000 {
+				ns := test.args.nodes
+				rand.Shuffle(len(ns), func(i, j int) {
+					ns[i], ns[j] = ns[j], ns[i]
+				})
+				us := users
+				rand.Shuffle(len(us), func(i, j int) {
+					us[i], us[j] = us[j], us[i]
+				})
+				got := filterNodesByUser(ns, us, test.args.user)
+				sort.Slice(got, func(i, j int) bool {
+					return got[i].ID < got[j].ID
+				})
 
 				if diff := cmp.Diff(test.want, got, util.Comparers...); diff != "" {
-				t.Errorf("listNodesInUser() = (-want +got):\n%s", diff)
+					t.Errorf("filterNodesByUser() = (-want +got):\n%s", diff)
+				}
 			}
 		})
 	}
@@ -940,6 +1191,12 @@ func Test_expandAlias(t *testing.T) {
 		return s
 	}
 
+	users := []types.User{
+		{Model: gorm.Model{ID: 1}, Name: "joe"},
+		{Model: gorm.Model{ID: 2}, Name: "marc"},
+		{Model: gorm.Model{ID: 3}, Name: "mickael"},
+	}
+
 	type field struct {
 		pol ACLPolicy
 	}
@@ -989,19 +1246,19 @@ func Test_expandAlias(t *testing.T) {
 				nodes: types.Nodes{
 					&types.Node{
 						IPv4: iap("100.64.0.1"),
-						User: types.User{Name: "joe"},
+						User: users[0],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.2"),
-						User: types.User{Name: "joe"},
+						User: users[0],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.3"),
-						User: types.User{Name: "marc"},
+						User: users[1],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.4"),
-						User: types.User{Name: "mickael"},
+						User: users[2],
 					},
 				},
 			},
@@ -1022,19 +1279,19 @@ func Test_expandAlias(t *testing.T) {
 				nodes: types.Nodes{
 					&types.Node{
 						IPv4: iap("100.64.0.1"),
-						User: types.User{Name: "joe"},
+						User: users[0],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.2"),
-						User: types.User{Name: "joe"},
+						User: users[0],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.3"),
-						User: types.User{Name: "marc"},
+						User: users[1],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.4"),
-						User: types.User{Name: "mickael"},
+						User: users[2],
 					},
 				},
 			},
@@ -1185,7 +1442,7 @@ func Test_expandAlias(t *testing.T) {
 				nodes: types.Nodes{
 					&types.Node{
 						IPv4: iap("100.64.0.1"),
-						User: types.User{Name: "joe"},
+						User: users[0],
 						Hostinfo: &tailcfg.Hostinfo{
 							OS:          "centos",
 							Hostname:    "foo",
@@ -1194,7 +1451,7 @@ func Test_expandAlias(t *testing.T) {
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.2"),
-						User: types.User{Name: "joe"},
+						User: users[0],
 						Hostinfo: &tailcfg.Hostinfo{
 							OS:          "centos",
 							Hostname:    "foo",
@@ -1203,11 +1460,11 @@ func Test_expandAlias(t *testing.T) {
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.3"),
-						User: types.User{Name: "marc"},
+						User: users[1],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.4"),
-						User: types.User{Name: "joe"},
+						User: users[0],
 					},
 				},
 			},
@@ -1260,21 +1517,21 @@ func Test_expandAlias(t *testing.T) {
 				nodes: types.Nodes{
 					&types.Node{
 						IPv4:       iap("100.64.0.1"),
-						User:       types.User{Name: "joe"},
+						User:       users[0],
 						ForcedTags: []string{"tag:hr-webserver"},
 					},
 					&types.Node{
 						IPv4:       iap("100.64.0.2"),
-						User:       types.User{Name: "joe"},
+						User:       users[0],
 						ForcedTags: []string{"tag:hr-webserver"},
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.3"),
-						User: types.User{Name: "marc"},
+						User: users[1],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.4"),
-						User: types.User{Name: "mickael"},
+						User: users[2],
 					},
 				},
 			},
@@ -1295,12 +1552,12 @@ func Test_expandAlias(t *testing.T) {
 				nodes: types.Nodes{
 					&types.Node{
 						IPv4:       iap("100.64.0.1"),
-						User:       types.User{Name: "joe"},
+						User:       users[0],
 						ForcedTags: []string{"tag:hr-webserver"},
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.2"),
-						User: types.User{Name: "joe"},
+						User: users[0],
 						Hostinfo: &tailcfg.Hostinfo{
 							OS:          "centos",
 							Hostname:    "foo",
@@ -1309,11 +1566,11 @@ func Test_expandAlias(t *testing.T) {
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.3"),
-						User: types.User{Name: "marc"},
+						User: users[1],
 					},
 					&types.Node{
 						IPv4: iap("100.64.0.4"),
-						User: types.User{Name: "mickael"},
+						User: users[2],
 					},
 				},
 			},
@@ -1350,12 +1607,12 @@ func Test_expandAlias(t *testing.T) {
 					},
 					&types.Node{
 						IPv4:     iap("100.64.0.3"),
-						User:     types.User{Name: "marc"},
+						User:     users[1],
 						Hostinfo: &tailcfg.Hostinfo{},
 					},
 					&types.Node{
 						IPv4:     iap("100.64.0.4"),
-						User:     types.User{Name: "joe"},
+						User:     users[0],
 						Hostinfo: &tailcfg.Hostinfo{},
 					},
 				},
@@ -1368,6 +1625,7 @@ func Test_expandAlias(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			got, err := test.field.pol.ExpandAlias(
 				test.args.nodes,
+				users,
 				test.args.alias,
 			)
 			if (err != nil) != test.wantErr {
@@ -1715,6 +1973,7 @@ func TestACLPolicy_generateFilterRules(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			got, err := tt.field.pol.CompileFilterRules(
+				[]types.User{},
 				tt.args.nodes,
 			)
 			if (err != nil) != tt.wantErr {
@@ -1842,6 +2101,13 @@ func TestTheInternet(t *testing.T) {
 }
 
 func TestReduceFilterRules(t *testing.T) {
+	users := []types.User{
+		{Model: gorm.Model{ID: 1}, Name: "mickael"},
+		{Model: gorm.Model{ID: 2}, Name: "user1"},
+		{Model: gorm.Model{ID: 3}, Name: "user2"},
+		{Model: gorm.Model{ID: 4}, Name: "user100"},
+	}
+
 	tests := []struct {
 		name  string
 		node  *types.Node
@@ -1863,13 +2129,13 @@ func TestReduceFilterRules(t *testing.T) {
 			node: &types.Node{
 				IPv4: iap("100.64.0.1"),
 				IPv6: iap("fd7a:115c:a1e0:ab12:4843:2222:6273:2221"),
-				User: types.User{Name: "mickael"},
+				User: users[0],
 			},
 			peers: types.Nodes{
 				&types.Node{
 					IPv4: iap("100.64.0.2"),
 					IPv6: iap("fd7a:115c:a1e0:ab12:4843:2222:6273:2222"),
-					User: types.User{Name: "mickael"},
+					User: users[0],
 				},
 			},
 			want: []tailcfg.FilterRule{},
@@ -1896,7 +2162,7 @@ func TestReduceFilterRules(t *testing.T) {
 			node: &types.Node{
 				IPv4: iap("100.64.0.1"),
 				IPv6: iap("fd7a:115c:a1e0::1"),
-				User: types.User{Name: "user1"},
+				User: users[1],
 				Hostinfo: &tailcfg.Hostinfo{
 					RoutableIPs: []netip.Prefix{
 						netip.MustParsePrefix("10.33.0.0/16"),
@@ -1907,7 +2173,7 @@ func TestReduceFilterRules(t *testing.T) {
 				&types.Node{
 					IPv4: iap("100.64.0.2"),
 					IPv6: iap("fd7a:115c:a1e0::2"),
-					User: types.User{Name: "user1"},
+					User: users[1],
 				},
 			},
 			want: []tailcfg.FilterRule{
@@ -1975,19 +2241,19 @@ func TestReduceFilterRules(t *testing.T) {
 			node: &types.Node{
 				IPv4: iap("100.64.0.1"),
 				IPv6: iap("fd7a:115c:a1e0::1"),
-				User: types.User{Name: "user1"},
+				User: users[1],
 			},
 			peers: types.Nodes{
 				&types.Node{
 					IPv4: iap("100.64.0.2"),
 					IPv6: iap("fd7a:115c:a1e0::2"),
-					User: types.User{Name: "user2"},
+					User: users[2],
 				},
 				// "internal" exit node
 				&types.Node{
 					IPv4: iap("100.64.0.100"),
 					IPv6: iap("fd7a:115c:a1e0::100"),
-					User: types.User{Name: "user100"},
+					User: users[3],
 					Hostinfo: &tailcfg.Hostinfo{
 						RoutableIPs: tsaddr.ExitRoutes(),
 					},
@@ -2034,12 +2300,12 @@ func TestReduceFilterRules(t *testing.T) {
 				&types.Node{
 					IPv4: iap("100.64.0.2"),
 					IPv6: iap("fd7a:115c:a1e0::2"),
-					User: types.User{Name: "user2"},
+					User: users[2],
 				},
 				&types.Node{
 					IPv4: iap("100.64.0.1"),
 					IPv6: iap("fd7a:115c:a1e0::1"),
-					User: types.User{Name: "user1"},
+					User: users[1],
 				},
 			},
 			want: []tailcfg.FilterRule{
@@ -2131,7 +2397,7 @@ func TestReduceFilterRules(t *testing.T) {
 			node: &types.Node{
 				IPv4: iap("100.64.0.100"),
 				IPv6: iap("fd7a:115c:a1e0::100"),
-				User: types.User{Name: "user100"},
+				User: users[3],
 				Hostinfo: &tailcfg.Hostinfo{
 					RoutableIPs: tsaddr.ExitRoutes(),
 				},
@@ -2140,12 +2406,12 @@ func TestReduceFilterRules(t *testing.T) {
 				&types.Node{
 					IPv4: iap("100.64.0.2"),
 					IPv6: iap("fd7a:115c:a1e0::2"),
-					User: types.User{Name: "user2"},
+					User: users[2],
 				},
 				&types.Node{
 					IPv4: iap("100.64.0.1"),
 					IPv6: iap("fd7a:115c:a1e0::1"),
-					User: types.User{Name: "user1"},
+					User: users[1],
 				},
 			},
 			want: []tailcfg.FilterRule{
@@ -2243,7 +2509,7 @@ func TestReduceFilterRules(t *testing.T) {
 			node: &types.Node{
 				IPv4: iap("100.64.0.100"),
 				IPv6: iap("fd7a:115c:a1e0::100"),
-				User: types.User{Name: "user100"},
+				User: users[3],
 				Hostinfo: &tailcfg.Hostinfo{
 					RoutableIPs: []netip.Prefix{
 						netip.MustParsePrefix("8.0.0.0/16"),
@@ -2255,12 +2521,12 @@ func TestReduceFilterRules(t *testing.T) {
 				&types.Node{
 					IPv4: iap("100.64.0.2"),
 					IPv6: iap("fd7a:115c:a1e0::2"),
-					User: types.User{Name: "user2"},
+					User: users[2],
 				},
 				&types.Node{
 					IPv4: iap("100.64.0.1"),
 					IPv6: iap("fd7a:115c:a1e0::1"),
-					User: types.User{Name: "user1"},
+					User: users[1],
 				},
 			},
 			want: []tailcfg.FilterRule{
@@ -2333,7 +2599,7 @@ func TestReduceFilterRules(t *testing.T) {
 			node: &types.Node{
 				IPv4: iap("100.64.0.100"),
 				IPv6: iap("fd7a:115c:a1e0::100"),
-				User: types.User{Name: "user100"},
+				User: users[3],
 				Hostinfo: &tailcfg.Hostinfo{
 					RoutableIPs: []netip.Prefix{
 						netip.MustParsePrefix("8.0.0.0/8"),
@@ -2345,12 +2611,12 @@ func TestReduceFilterRules(t *testing.T) {
 				&types.Node{
 					IPv4: iap("100.64.0.2"),
 					IPv6: iap("fd7a:115c:a1e0::2"),
-					User: types.User{Name: "user2"},
+					User: users[2],
 				},
 				&types.Node{
 					IPv4: iap("100.64.0.1"),
 					IPv6: iap("fd7a:115c:a1e0::1"),
-					User: types.User{Name: "user1"},
+					User: users[1],
 				},
 			},
 			want: []tailcfg.FilterRule{
@@ -2416,7 +2682,7 @@ func TestReduceFilterRules(t *testing.T) {
 			node: &types.Node{
 				IPv4: iap("100.64.0.100"),
 				IPv6: iap("fd7a:115c:a1e0::100"),
-				User: types.User{Name: "user100"},
+				User: users[3],
 				Hostinfo: &tailcfg.Hostinfo{
 					RoutableIPs: []netip.Prefix{netip.MustParsePrefix("172.16.0.0/24")},
 				},
@@ -2426,7 +2692,7 @@ func TestReduceFilterRules(t *testing.T) {
 				&types.Node{
 					IPv4: iap("100.64.0.1"),
 					IPv6: iap("fd7a:115c:a1e0::1"),
-					User: types.User{Name: "user1"},
+					User: users[1],
 				},
 			},
 			want: []tailcfg.FilterRule{
@@ -2454,6 +2720,7 @@ func TestReduceFilterRules(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			got, _ := tt.pol.CompileFilterRules(
+				users,
 				append(tt.peers, tt.node),
 			)
 
@@ -3461,7 +3728,7 @@ func TestSSHRules(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got, err := tt.pol.CompileSSHPolicy(&tt.node, tt.peers)
+			got, err := tt.pol.CompileSSHPolicy(&tt.node, []types.User{}, tt.peers)
 			require.NoError(t, err)
 
 			if diff := cmp.Diff(tt.want, got); diff != "" {
@@ -3544,14 +3811,17 @@ func TestValidExpandTagOwnersInSources(t *testing.T) {
 		RequestTags: []string{"tag:test"},
 	}
 
+	user := types.User{
+		Model: gorm.Model{ID: 1},
+		Name:  "user1",
+	}
+
 	node := &types.Node{
 		ID:             0,
 		Hostname:       "testnodes",
 		IPv4:           iap("100.64.0.1"),
 		UserID:         0,
-		User: types.User{
+		User:           user,
-			Name: "user1",
-		},
 		RegisterMethod: util.RegisterMethodAuthKey,
 		Hostinfo:       &hostInfo,
 	}
@@ -3568,7 +3838,7 @@ func TestValidExpandTagOwnersInSources(t *testing.T) {
 		},
 	}
 
-	got, _, err := GenerateFilterAndSSHRulesForTests(pol, node, types.Nodes{})
+	got, _, err := GenerateFilterAndSSHRulesForTests(pol, node, types.Nodes{}, []types.User{user})
 	require.NoError(t, err)
 
 	want := []tailcfg.FilterRule{
@@ -3602,6 +3872,7 @@ func TestInvalidTagValidUser(t *testing.T) {
 		IPv4:     iap("100.64.0.1"),
 		UserID:   1,
 		User: types.User{
+			Model: gorm.Model{ID: 1},
 			Name:  "user1",
 		},
 		RegisterMethod: util.RegisterMethodAuthKey,
@@ -3619,7 +3890,12 @@ func TestInvalidTagValidUser(t *testing.T) {
 		},
 	}
 
-	got, _, err := GenerateFilterAndSSHRulesForTests(pol, node, types.Nodes{})
+	got, _, err := GenerateFilterAndSSHRulesForTests(
+		pol,
+		node,
+		types.Nodes{},
+		[]types.User{node.User},
+	)
 	require.NoError(t, err)
 
 	want := []tailcfg.FilterRule{
@@ -3653,6 +3929,7 @@ func TestValidExpandTagOwnersInDestinations(t *testing.T) {
 		IPv4:     iap("100.64.0.1"),
 		UserID:   1,
 		User: types.User{
+			Model: gorm.Model{ID: 1},
 			Name:  "user1",
 		},
 		RegisterMethod: util.RegisterMethodAuthKey,
@@ -3678,7 +3955,12 @@ func TestValidExpandTagOwnersInDestinations(t *testing.T) {
 	// c.Assert(rules[0].DstPorts, check.HasLen, 1)
 	// c.Assert(rules[0].DstPorts[0].IP, check.Equals, "100.64.0.1/32")
 
-	got, _, err := GenerateFilterAndSSHRulesForTests(pol, node, types.Nodes{})
+	got, _, err := GenerateFilterAndSSHRulesForTests(
+		pol,
+		node,
+		types.Nodes{},
+		[]types.User{node.User},
+	)
 	require.NoError(t, err)
 
 	want := []tailcfg.FilterRule{
@@ -3707,15 +3989,17 @@ func TestValidTagInvalidUser(t *testing.T) {
 		Hostname:    "webserver",
 		RequestTags: []string{"tag:webapp"},
 	}
+	user := types.User{
+		Model: gorm.Model{ID: 1},
+		Name:  "user1",
+	}
 
 	node := &types.Node{
 		ID:             1,
 		Hostname:       "webserver",
 		IPv4:           iap("100.64.0.1"),
 		UserID:         1,
-		User: types.User{
+		User:           user,
-			Name: "user1",
-		},
 		RegisterMethod: util.RegisterMethodAuthKey,
 		Hostinfo:       &hostInfo,
 	}
@@ -3730,9 +4014,7 @@ func TestValidTagInvalidUser(t *testing.T) {
 		Hostname:       "user",
 		IPv4:           iap("100.64.0.2"),
 		UserID:         1,
-		User: types.User{
+		User:           user,
-			Name: "user1",
-		},
 		RegisterMethod: util.RegisterMethodAuthKey,
 		Hostinfo:       &hostInfo2,
 	}
@@ -3748,7 +4030,12 @@ func TestValidTagInvalidUser(t *testing.T) {
 		},
 	}
 
-	got, _, err := GenerateFilterAndSSHRulesForTests(pol, node, types.Nodes{nodes2})
+	got, _, err := GenerateFilterAndSSHRulesForTests(
+		pol,
+		node,
+		types.Nodes{nodes2},
+		[]types.User{user},
+	)
 	require.NoError(t, err)
 
 	want := []tailcfg.FilterRule{

hscontrol/types/users.go

@@ -3,6 +3,7 @@ package types
 import (
 	"cmp"
 	"database/sql"
+	"net/mail"
 	"strconv"
 
 	v1 "github.com/juanfont/headscale/gen/go/headscale/v1"
@@ -56,14 +57,7 @@ type User struct {
 // should be used throughout headscale, in information returned to the
 // user and the Policy engine.
 func (u *User) Username() string {
-	username := cmp.Or(u.Email, u.Name, u.ProviderIdentifier.String, strconv.FormatUint(uint64(u.ID), 10))
+	return cmp.Or(u.Email, u.Name, u.ProviderIdentifier.String, strconv.FormatUint(uint64(u.ID), 10))
-
-	// TODO(kradalby): Wire up all of this for the future
-	// if !strings.Contains(username, "@") {
-	// 	username = username + "@"
-	// }
-
-	return username
 }
 
 // DisplayNameOrUsername returns the DisplayName if it exists, otherwise
@@ -146,12 +140,20 @@ func (c *OIDCClaims) Identifier() string {
 // FromClaim overrides a User from OIDC claims.
 // All fields will be updated, except for the ID.
 func (u *User) FromClaim(claims *OIDCClaims) {
-	u.ProviderIdentifier = sql.NullString{String: claims.Identifier(), Valid: true}
+	err := util.CheckForFQDNRules(claims.Username)
-	u.DisplayName = claims.Name
+	if err == nil {
+		u.Name = claims.Username
+	}
+
 	if claims.EmailVerified {
+		_, err = mail.ParseAddress(claims.Email)
+		if err == nil {
 			u.Email = claims.Email
 		}
-	u.Name = claims.Username
+	}
+
+	u.ProviderIdentifier = sql.NullString{String: claims.Identifier(), Valid: true}
+	u.DisplayName = claims.Name
 	u.ProfilePicURL = claims.ProfilePictureURL
 	u.Provider = util.RegisterMethodOIDC
 }