fix: resolve sign-in authentication failure

[milanbeherazyx]

Problem

The __auth method in main.py silently fails with error while signin, causing all authenticated users to fall back to unauthorized_user_token (no-login mode). This has been a widely reported issue affecting many users.

Root Cause

The existing implementation uses a bare requests.post() call without:

• A User-Agent header — TradingView flags the request as bot traffic
• A requests.Session() — No cookies are persisted, triggering rate-limit / anti-bot protection
• Proper Origin and Content-Type headers

As a result, TradingView returns a rate_limit error or silently rejects the sign-in request.

Fix

Updated the __auth method to properly authenticate with TradingView:

• Use requests.Session() to maintain cookies across the GET → POST flow
• Set a browser-like User-Agent to avoid bot detection
• Visit the homepage first (GET /) before posting to /accounts/signin/ to establish a proper session
• Add Origin and Content-Type headers for CORS compliance
• Add a single retry with 2s delay when rate-limited
• Improved error logging to include the actual exception message for easier debugging
• Removed duplicate import json statement

Before (Broken)

error while signin
you are using nologin method, data you access may be limited
Token: unauthorized_user_token

After (Fixed)

https://www.tradingview.com:443 "GET / HTTP/1.1" 200
https://www.tradingview.com:443 "POST /accounts/signin/ HTTP/1.1" 200
Token: eyJhbGciOiJSUzUxMiIs...  (valid JWT auth token)

Testing

Tested with valid TradingView credentials — login now succeeds and returns a proper JWT auth_token. Data fetching with authenticated session works as expected (verified with NIFTY 15-min candles from NSE).

Backward Compatibility

• No API changes — TvDatafeed(username, password) works the same way
• No-login mode (TvDatafeed()) is unaffected
• No new dependencies added