: Enable logging on the token exchange but redact code_verifier and refresh_token before persisting. 7. Comparison with Other Accounting APIs | Feature | lexoffice | DATEV | Xero | QuickBooks | |---------|-----------|-------|------|-------------| | OAuth2 | ✅ PKCE | ✅ PKCE | ✅ PKCE | ✅ PKCE | | Refresh token rotation | ✅ (recommended) | ❌ | ✅ | ✅ | | Sandbox environment | ✅ | ✅ | ✅ | ✅ | | Scope discovery via metadata | ✅ OIDC Discovery | ❌ | ✅ | ✅ |
# Exchange data = "grant_type": "authorization_code", "code": auth_code, "redirect_uri": self.redirect_uri, "client_id": self.client_id, "code_verifier": self.code_verifier resp = requests.post(self.TOKEN_URL, data=data) resp.raise_for_status() tokens = resp.json() return tokens # contains access_token, refresh_token, expires_in lexoffice.login
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)" : Enable logging on the token exchange but
Abstract Modern cloud accounting platforms like lexoffice provide RESTful APIs for integrating financial data into third-party applications. A critical component is the authentication flow, typically encapsulated as lexoffice.login . This paper analyzes the design, implementation, and security considerations of lexoffice’s login mechanism based on OAuth 2.0 with Proof Key for Code Exchange (PKCE). We present a reference implementation, discuss common integration pitfalls, and evaluate the trade-offs between security and usability. The findings provide a blueprint for developers integrating lexoffice or similar FinTech APIs. A critical component is the authentication flow, typically
"access_token": "eyJhbGciOiJSUzI1NiIs...", "token_type": "Bearer", "expires_in": 3600, "refresh_token": "8xLOxBtZp8...", "scope": "invoice.read contact.read openid profile"
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
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