Future work could explore automated refresh token handling and background token refresh in SPAs using Web Workers. The principles outlined here are transferable to any OAuth2‑protected financial API. [1] lexoffice API Documentation. Authentication . Retrieved from https://developers.lexoffice.io/docs/#authentication [2] IETF RFC 6749 – The OAuth 2.0 Authorization Framework. [3] IETF RFC 7636 – Proof Key for Code Exchange (PKCE). [4] OWASP. OAuth 2.0 Security Cheat Sheet . [5] lexoffice OpenID Configuration – https://login.lexoffice.io/.well-known/openid-configuration Appendix – Full Token Response Example
def get_login_url(self): """Return the URL to redirect the user for lexoffice login.""" self.state = secrets.token_urlsafe(16) challenge = self._generate_pkce_pair() params = "response_type": "code", "client_id": self.client_id, "redirect_uri": self.redirect_uri, "scope": " ".join(self.scopes), "state": self.state, "code_challenge": challenge, "code_challenge_method": "S256" return f"self.AUTH_URL?urlencode(params)"
– The author declares no affiliation with lexoffice GmbH. This paper is for educational purposes. This paper provides a complete, actionable analysis of lexoffice.login suitable for a developer audience, a software architecture review, or a student project in API security.
def __init__(self, client_id, redirect_uri, scopes=None): self.client_id = client_id self.redirect_uri = redirect_uri self.scopes = scopes or ["openid", "profile", "invoice.read"] self.code_verifier = None self.state = None
def handle_callback(self, callback_url): """Parse callback, verify state, exchange code for tokens.""" parsed = urlparse(callback_url) query = parse_qs(parsed.query) if "state" not in query or query["state"][0] != self.state: raise ValueError("Invalid state parameter – possible CSRF attack") if "code" not in query: raise ValueError("No authorization code received") auth_code = query["code"][0]