feat: show API key SHA256 hash instead of asterisk masking

Replace the generic asterisk masking with a deterministic SHA256 hash
prefix to allow developers to verify which API key is being used while
maintaining security.

Changes:
- Add hashlib import for SHA256 support
- Create openai_api_key_hash helper property
- Update config display to show: API_KEY=sha256:<hash_prefix>...

Author: elifarley

src/core/config.py

@@ -1,5 +1,6 @@
 import os
 import sys
+import hashlib
 
 # Configuration
 class Config:
@@ -69,9 +70,20 @@ def get_custom_headers(self):
 
         return custom_headers
 
+    @property
+    def openai_api_key_hash(self):
+        """Get the first few characters of SHA256 hash of the OpenAI API key.
+
+        This provides a secure way to identify the API key without exposing it.
+        Returns '<not-set>' if the API key is not configured.
+
+        Returns:
+            str: First few characters of SHA256 hash or '<not-set>'
+        """
+        return "<not-set>" if not self.openai_api_key else 'sha256:' + hashlib.sha256(self.openai_api_key.encode()).hexdigest()[:16] + '...'
+
 try:
     config = Config()
-    print(f" Configuration loaded: API_KEY={'*' * 20}..., BASE_URL='{config.openai_base_url}'")
 except Exception as e:
     print(f"=4 Configuration Error: {e}")
     sys.exit(1)

src/main.py

@@ -42,12 +42,13 @@ def main():
     # Configuration summary
     print("🚀 Claude-to-OpenAI API Proxy v1.0.0")
     print(f"✅ Configuration loaded successfully")
+    print(f"   OpenAI API Key : {config.openai_api_key_hash}")
     print(f"   OpenAI Base URL: {config.openai_base_url}")
     print(f"   Big Model (opus): {config.big_model}")
     print(f"   Middle Model (sonnet): {config.middle_model}")
     print(f"   Small Model (haiku): {config.small_model}")
     print(f"   Max Tokens Limit: {config.max_tokens_limit}")
-    print(f"   Request Timeout: {config.request_timeout}s")
+    print(f"   Request Timeout : {config.request_timeout}s")
     print(f"   Server: {config.host}:{config.port}")
     print(f"   Client API Key Validation: {'Enabled' if config.anthropic_api_key else 'Disabled'}")
     print("")