fix: use ActiveDirectoryDefault for -G with no username

When -G is passed without a username, sqlcmd was selecting ActiveDirectoryIntegrated (Windows SSPI), which requires an interactive logon token and fails in non-interactive contexts like Emacs inferior shells or CI jobs with 'Integrated Security not supported'.

Switch to ActiveDirectoryDefault, which walks the standard Azure credential chain (env vars, managed identity, Azure CLI, VS, then interactive browser). This matches the existing -G help text and works across Windows/Linux/macOS. Users who specifically need SSPI can still pass --authentication-method=ActiveDirectoryIntegrated.

Fixes #699

Author: dlevy-msft-sql

cmd/sqlcmd/sqlcmd.go

@@ -203,7 +203,8 @@ func (a SQLCmdArguments) authenticationMethod(hasPassword bool) string {
 	if a.UseAad {
 		switch {
 		case a.UserName == "":
-			return azuread.ActiveDirectoryIntegrated
+			// Default walks the Azure credential chain; works in non-interactive shells (issue #699).
+			return azuread.ActiveDirectoryDefault
 		case hasPassword:
 			return azuread.ActiveDirectoryPassword
 		default:

cmd/sqlcmd/sqlcmd_test.go

@@ -519,6 +519,26 @@ func TestConditionsForPasswordPrompt(t *testing.T) {
 	}
 }
 
+func TestAuthenticationMethodForUseAad(t *testing.T) {
+	tests := []struct {
+		name        string
+		userName    string
+		hasPassword bool
+		expected    string
+	}{
+		{"-G no username picks Default", "", false, azuread.ActiveDirectoryDefault},
+		{"-G no username, password ignored", "", true, azuread.ActiveDirectoryDefault},
+		{"-G with username, no password picks Interactive", "user@contoso", false, azuread.ActiveDirectoryInteractive},
+		{"-G with username and password picks Password", "user@contoso", true, azuread.ActiveDirectoryPassword},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			a := SQLCmdArguments{UseAad: true, UserName: tc.userName}
+			assert.Equal(t, tc.expected, a.authenticationMethod(tc.hasPassword))
+		})
+	}
+}
+
 func TestStartupScript(t *testing.T) {
 	o, err := os.CreateTemp("", "sqlcmdmain")
 	assert.NoError(t, err, "os.CreateTemp")