Lexoffice.login May 2026

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.

lexoffice’s strength is strict PKCE enforcement and well‑structured OpenID Connect Discovery ( /.well-known/openid-configuration ). The lexoffice.login mechanism is a robust implementation of OAuth 2.0 + PKCE, suitable for both server‑side and public client applications. Developers must correctly generate the PKCE pair, validate the state parameter, and store tokens securely. By following the reference implementation and security recommendations in this paper, integration can achieve both usability and a high security level.

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)" lexoffice.login

import hashlib import secrets import requests from urllib.parse import urlencode, urlparse, parse_qs class LexofficeLogin: AUTH_URL = "https://login.lexoffice.io/connect/authorize" TOKEN_URL = "https://login.lexoffice.io/connect/token"

"access_token": "eyJhbGciOiJSUzI1NiIs...", "token_type": "Bearer", "expires_in": 3600, "refresh_token": "8xLOxBtZp8...", "scope": "invoice.read contact.read openid profile" The lexoffice

# 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

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 "scope": " ".join(self.scopes)

: 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 | ❌ | ✅ | ✅ |