fix: improve LDAP error handling (#425)

Co-authored-by: Kyle Mendell <kmendell@ofkm.us>

backend/internal/service/ldap_service_test.go

@@ -0,0 +1,73 @@
+package service
+
+import (
+	"testing"
+)
+
+func TestGetDNProperty(t *testing.T) {
+	tests := []struct {
+		name           string
+		property       string
+		dn             string
+		expectedResult string
+	}{
+		{
+			name:           "simple case",
+			property:       "cn",
+			dn:             "cn=username,ou=people,dc=example,dc=com",
+			expectedResult: "username",
+		},
+		{
+			name:           "property not found",
+			property:       "uid",
+			dn:             "cn=username,ou=people,dc=example,dc=com",
+			expectedResult: "",
+		},
+		{
+			name:           "mixed case property",
+			property:       "CN",
+			dn:             "cn=username,ou=people,dc=example,dc=com",
+			expectedResult: "username",
+		},
+		{
+			name:           "mixed case DN",
+			property:       "cn",
+			dn:             "CN=username,OU=people,DC=example,DC=com",
+			expectedResult: "username",
+		},
+		{
+			name:           "spaces in DN",
+			property:       "cn",
+			dn:             "cn=username, ou=people, dc=example, dc=com",
+			expectedResult: "username",
+		},
+		{
+			name:           "value with special characters",
+			property:       "cn",
+			dn:             "cn=user.name+123,ou=people,dc=example,dc=com",
+			expectedResult: "user.name+123",
+		},
+		{
+			name:           "empty DN",
+			property:       "cn",
+			dn:             "",
+			expectedResult: "",
+		},
+		{
+			name:           "empty property",
+			property:       "",
+			dn:             "cn=username,ou=people,dc=example,dc=com",
+			expectedResult: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := getDNProperty(tt.property, tt.dn)
+			if result != tt.expectedResult {
+				t.Errorf("getDNProperty(%q, %q) = %q, want %q",
+					tt.property, tt.dn, result, tt.expectedResult)
+			}
+		})
+	}
+}