feat(providers): add OAuth token detection and header utilities

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nanobot/providers/oauth_utils.py

@@ -0,0 +1,46 @@
+"""OAuth utility functions for Anthropic subscription auth."""
+
+from typing import Any
+
+
+def is_oauth_token(token: str | None) -> bool:
+    """Check if token is an OAuth token (vs regular API key).
+
+    OAuth tokens from Claude Max/Pro contain 'sk-ant-oat' prefix.
+    Regular API keys use 'sk-ant-api03' or similar.
+    """
+    if not token:
+        return False
+    return "sk-ant-oat" in token
+
+
+def get_auth_headers(token: str, is_oauth: bool = False) -> dict[str, str]:
+    """Get authentication headers for Anthropic API.
+
+    OAuth tokens require Authorization: Bearer header.
+    Regular API keys use x-api-key header.
+    """
+    headers: dict[str, str] = {
+        "anthropic-version": "2023-06-01",
+        "content-type": "application/json",
+    }
+
+    if is_oauth:
+        headers["Authorization"] = f"Bearer {token}"
+        # Required headers to mimic Claude Code client
+        headers["anthropic-beta"] = "claude-code-20250219,oauth-2025-04-20"
+        headers["anthropic-dangerous-direct-browser-access"] = "true"
+        headers["user-agent"] = "claude-cli/2.1.2 (external, cli)"
+        headers["x-app"] = "cli"
+    else:
+        headers["x-api-key"] = token
+
+    return headers
+
+
+def get_claude_code_system_prefix() -> str:
+    """Get the required system prompt prefix for OAuth tokens.
+
+    Anthropic requires this identity declaration for OAuth auth.
+    """
+    return "You are Claude Code, Anthropic's official CLI for Claude."

tests/test_oauth_utils.py

@@ -0,0 +1,28 @@
+"""Test OAuth utility functions."""
+import pytest
+from nanobot.providers.oauth_utils import is_oauth_token, get_auth_headers
+
+
+def test_is_oauth_token_detects_oat():
+    """Should detect sk-ant-oat tokens as OAuth."""
+    assert is_oauth_token("sk-ant-oat01-buSdhCH2XEkebW7ZQZTvGqH5EwAFh4u52LrdJhAP") is True
+    assert is_oauth_token("sk-ant-api03-regularkey") is False
+    assert is_oauth_token("") is False
+    assert is_oauth_token(None) is False
+
+
+def test_get_auth_headers_oauth():
+    """OAuth tokens should use Authorization: Bearer."""
+    headers = get_auth_headers("sk-ant-oat01-xxx", is_oauth=True)
+    assert "Authorization" in headers
+    assert headers["Authorization"] == "Bearer sk-ant-oat01-xxx"
+    assert "x-api-key" not in headers
+    assert headers["anthropic-beta"] == "claude-code-20250219,oauth-2025-04-20"
+
+
+def test_get_auth_headers_api_key():
+    """Regular API keys should use x-api-key."""
+    headers = get_auth_headers("sk-ant-api03-xxx", is_oauth=False)
+    assert "x-api-key" in headers
+    assert headers["x-api-key"] == "sk-ant-api03-xxx"
+    assert "Authorization" not in headers