policy/v2: trim whitespace in SSH src and dst aliases

SaaS trims surrounding whitespace from src/dst entries before
dispatching to the alias lookup, so `"tag:server "` resolves to the
same tag and `" odin@example.com"` resolves to the same user.
headscale was treating the untrimmed strings as literals, which
either failed the tag/user lookup or dropped the affected node from
every rule referencing it. Trim inside AliasEnc.UnmarshalJSON so
ACL src/dst and SSH src/dst all benefit.

hscontrol/policy/v2/tailscale_ssh_data_compat_test.go

@@ -88,19 +88,6 @@ var sshSkipReasons = map[string]string{
 	"ssh-b5":  "user:*@passkey wildcard not supported in headscale",
 	"ssh-d10": "user:*@passkey wildcard not supported in headscale",
 
-	// WHITESPACE_TRIM_IN_SRC_DST (2 tests)
-	//
-	// SaaS strips surrounding whitespace from SSH rule src/dst entries
-	// before lookup ("tag:server " resolves to "tag:server",
-	// " user@host" resolves to "user@host"). headscale treats the
-	// untrimmed string as a literal identifier and either fails the
-	// tag/user lookup or produces no rule for the affected node. The
-	// fix lives in policy/v2 alias resolution — strings.TrimSpace at
-	// the same point where SaaS does, before dispatching to the alias
-	// type registry.
-	"ssh-dst-trailing-whitespace": "src/dst whitespace trim mismatch: SaaS trims, headscale doesn't",
-	"ssh-src-leading-whitespace":  "src/dst whitespace trim mismatch: SaaS trims, headscale doesn't",
-
 	// TAG_OWNER_CYCLE_TOLERATED (2 tests)
 	//
 	// SaaS accepts tagOwners with circular references (tag:a -> tag:b,

hscontrol/policy/v2/types.go

@@ -1043,10 +1043,17 @@ func parseAlias(vs string) (Alias, error) {
 // AliasEnc is used to deserialize a Alias.
 type AliasEnc struct{ Alias }
 
+// UnmarshalJSON trims surrounding whitespace from each alias string
+// before dispatching so that `"tag:server "` or `" odin@example.com"`
+// resolves to the same tag or user SaaS would resolve. SaaS trims
+// before lookup; a literal-match policy here would drop the affected
+// node from every rule referencing it.
 func (ve *AliasEnc) UnmarshalJSON(b []byte) error {
 	ptr, err := unmarshalPointer(
 		b,
-		parseAlias,
+		func(s string) (Alias, error) {
+			return parseAlias(strings.TrimSpace(s))
+		},
 	)
 	if err != nil {
 		return err

hscontrol/policy/v2/types_test.go

@@ -4787,6 +4787,55 @@ func TestSSHUserTrimEndToEnd(t *testing.T) {
 	})
 }
 
+// TestAliasEncUnmarshalTrim verifies that src/dst entries get
+// trimmed before alias dispatch so `"tag:server "` resolves to the
+// same Tag alias SaaS uses and `" odin@example.com"` resolves to the
+// same Username alias. Covers tag, group, user, and autogroup entries
+// on both the leading- and trailing-whitespace edges.
+func TestAliasEncUnmarshalTrim(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  Alias
+	}{
+		{
+			name:  "tag trailing whitespace",
+			input: `"tag:server "`,
+			want:  new(Tag("tag:server")),
+		},
+		{
+			name:  "tag leading whitespace",
+			input: `" tag:server"`,
+			want:  new(Tag("tag:server")),
+		},
+		{
+			name:  "group leading whitespace",
+			input: `" group:admins"`,
+			want:  new(Group("group:admins")),
+		},
+		{
+			name:  "user trailing whitespace",
+			input: `"odin@example.com "`,
+			want:  new(Username("odin@example.com")),
+		},
+		{
+			name:  "autogroup trailing whitespace",
+			input: `"autogroup:member "`,
+			want:  new(AutoGroup("autogroup:member")),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var a AliasEnc
+
+			err := json.Unmarshal([]byte(tt.input), &a)
+			require.NoError(t, err)
+			require.Equal(t, tt.want, a.Alias)
+		})
+	}
+}
+
 // TestSSHCheckPeriodInvalidDuration verifies the SaaS body for the
 // malformed-duration case (`time: invalid duration "abc"`).
 func TestSSHCheckPeriodInvalidDuration(t *testing.T) {