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feat: add anthropic billing bypass patch module

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Kristian Vastveit 2026-04-12 15:01:25 +02:00
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"""
Claude Code OAuth bypass for hermes-agent.
==========================================
Monkey-patches hermes-agent's ``agent.anthropic_adapter.build_anthropic_kwargs``
at import time via a sitecustomize.py hook so that OAuth-authenticated requests
pass Anthropic's server-side content validation.
Background
----------
On 2026-04-04 Anthropic deployed server-side validation on OAuth requests: if
the ``system[]`` array contains text that doesn't match Claude Code's system
prompt structure, the request is rejected with HTTP 400 — even on accounts with
remaining subscription quota. Third-party tools (hermes-agent, opencode, cline,
aider, etc.) all hit this simultaneously.
opencode-claude-auth v1.4.8 (PR #148) worked around it by:
1. Injecting a cryptographically-signed ``x-anthropic-billing-header`` as
``system[0]``. The signature is derived from characters at positions 4, 7,
20 of the first user message, a hardcoded salt, and the Claude CLI version.
2. Relocating all non-Claude-Code system prompt content to the first user
message wrapped in ``<system-reminder>`` blocks.
3. Adding the ``prompt-caching-scope-2026-01-05`` beta flag.
hermes-agent already implements the Claude Code identity prefix, user-agent
spoofing, ``x-app: cli``, tool name ``mcp_`` prefixing, and the
``oauth-2025-04-20`` / ``claude-code-20250219`` beta flags. This patch adds
only the three items above plus a temperature fix for Opus 4.6 adaptive thinking.
Installation
------------
Installed automatically by ``install.sh``. See README.md for details.
The ``sitecustomize_hook.py`` loader runs at Python interpreter startup and
hooks ``agent.anthropic_adapter``'s import so that ``apply_patches()`` runs
immediately after the module is loaded. No hermes-agent source modifications
are needed.
Reversal
--------
Run ``uninstall.sh`` or manually remove the sitecustomize hook from the venv's
site-packages and restart hermes-gateway.
References
----------
- https://github.com/griffinmartin/opencode-claude-auth
- https://github.com/griffinmartin/opencode-claude-auth/pull/148
Version history
---------------
- 1.0.0 (2026-04-09): Initial — billing header, system prompt relocation,
prompt-caching beta flag, aux-client temperature hook for Opus 4.6.
"""
from __future__ import annotations
__version__ = "1.0.0"
import hashlib
import inspect
import logging
import sys
import traceback
from typing import Any, Dict, List
logger = logging.getLogger("anthropic_billing_bypass")
# ---------------------------------------------------------------------------
# Cryptographic signing (ported from opencode-claude-auth/src/signing.ts)
# ---------------------------------------------------------------------------
# Shared secret shipped in the Claude Code CLI binary. Anthropic's server
# uses this salt to verify billing-header signatures.
_BILLING_SALT = "59cf53e54c78"
# Sentinel strings — entries in system[] starting with these are kept;
# everything else is relocated to the first user message.
_BILLING_PREFIX = "x-anthropic-billing-header"
_SYSTEM_IDENTITY = "You are Claude Code, Anthropic's official CLI for Claude."
def _extract_first_user_message_text(messages: List[Dict[str, Any]]) -> str:
"""Return the text of the first user message's first text block.
Matches Claude Code's K19() exactly: find the first message with
role="user", then return the text of its first text content block.
"""
for msg in messages:
if not isinstance(msg, dict) or msg.get("role") != "user":
continue
content = msg.get("content")
if isinstance(content, str):
return content
if isinstance(content, list):
for block in content:
if isinstance(block, dict) and block.get("type") == "text":
text = block.get("text")
if isinstance(text, str) and text:
return text
return ""
return ""
def _compute_cch(message_text: str) -> str:
"""First 5 hex chars of SHA-256(message_text)."""
return hashlib.sha256(message_text.encode("utf-8")).hexdigest()[:5]
def _compute_version_suffix(message_text: str, version: str) -> str:
"""3-char version suffix: SHA-256(salt + sampled_chars + version)[:3].
Samples characters at indices 4, 7, 20 from the message text, padding
with "0" when the message is shorter than the index.
"""
sampled = "".join(
message_text[i] if i < len(message_text) else "0" for i in (4, 7, 20)
)
input_str = f"{_BILLING_SALT}{sampled}{version}"
return hashlib.sha256(input_str.encode("utf-8")).hexdigest()[:3]
def _build_billing_header_value(
messages: List[Dict[str, Any]],
version: str,
entrypoint: str,
) -> str:
"""Build the full x-anthropic-billing-header text for system[0]."""
text = _extract_first_user_message_text(messages)
suffix = _compute_version_suffix(text, version)
cch = _compute_cch(text)
return (
f"x-anthropic-billing-header: "
f"cc_version={version}.{suffix}; "
f"cc_entrypoint={entrypoint}; "
f"cch={cch};"
)
# ---------------------------------------------------------------------------
# Bypass logic (ported from opencode-claude-auth/src/transforms.ts)
# ---------------------------------------------------------------------------
def _model_supports_adaptive_thinking(model: str) -> bool:
if not isinstance(model, str):
return False
return any(v in model for v in ("4-6", "4.6"))
def _fix_temperature_for_oauth_adaptive(
api_kwargs: Dict[str, Any],
*,
site: str,
) -> None:
"""Strip temperature from OAuth requests on adaptive-thinking models.
Opus 4.6 with implicit adaptive thinking rejects non-1 temperature
values with HTTP 400. This drops the parameter entirely so the API
uses its default.
"""
if "temperature" not in api_kwargs:
return
temp = api_kwargs.get("temperature")
if temp == 1 or temp == 1.0:
return
model = api_kwargs.get("model")
if not _model_supports_adaptive_thinking(model or ""):
return
del api_kwargs["temperature"]
logger.info(
"Dropped temperature=%r for OAuth adaptive-thinking model %r (site=%s)",
temp,
model,
site,
)
def _prepend_to_first_user_message(
messages: List[Dict[str, Any]],
texts: List[str],
) -> None:
"""Prepend each text as a <system-reminder> block to the first user message.
Mutates ``messages`` in place.
"""
if not texts:
return
combined = "\n\n".join(f"<system-reminder>\n{t}\n</system-reminder>" for t in texts)
for i, msg in enumerate(messages):
if not isinstance(msg, dict) or msg.get("role") != "user":
continue
content = msg.get("content")
if isinstance(content, str):
new_text = f"{combined}\n\n{content}" if content else combined
messages[i] = {**msg, "content": [{"type": "text", "text": new_text}]}
return
if isinstance(content, list):
new_content = list(content)
for j, block in enumerate(new_content):
if isinstance(block, dict) and block.get("type") == "text":
existing = block.get("text") or ""
new_content[j] = {
**block,
"text": f"{combined}\n\n{existing}" if existing else combined,
}
messages[i] = {**msg, "content": new_content}
return
new_content.insert(0, {"type": "text", "text": combined})
messages[i] = {**msg, "content": new_content}
return
messages[i] = {**msg, "content": [{"type": "text", "text": combined}]}
return
def apply_claude_code_bypass(api_kwargs: Dict[str, Any], version: str) -> None:
"""Mutate api_kwargs in place to pass OAuth content validation.
Only call on OAuth requests (``is_oauth=True``). Safe to call multiple
times — stale billing headers are replaced, duplicate identity entries
are dropped.
After this runs, ``api_kwargs["system"]`` contains at most the billing
header and the Claude Code identity prefix. Everything else is moved to
the first user message as ``<system-reminder>`` blocks.
"""
messages = api_kwargs.get("messages")
if not isinstance(messages, list) or not messages:
return
raw_system = api_kwargs.get("system")
if raw_system is None:
system: List[Any] = []
elif isinstance(raw_system, str):
system = [{"type": "text", "text": raw_system}] if raw_system else []
elif isinstance(raw_system, list):
system = list(raw_system)
else:
logger.warning(
"Unexpected system type %s; skipping bypass", type(raw_system).__name__
)
return
# Compute billing header using ORIGINAL messages (before relocation).
try:
billing_value = _build_billing_header_value(messages, version, "cli")
except Exception as exc:
logger.warning("Failed to build billing header: %s", exc)
return
billing_entry = {"type": "text", "text": billing_value}
kept: List[Any] = []
moved_texts: List[str] = []
identity_seen = False
for entry in system:
if not isinstance(entry, dict):
kept.append(entry)
continue
entry_type = entry.get("type")
if entry_type != "text":
kept.append(entry)
continue
text = entry.get("text") or ""
if text.startswith(_BILLING_PREFIX):
continue # stale billing header — drop
if text.startswith(_SYSTEM_IDENTITY):
if identity_seen:
continue # duplicate — drop
identity_seen = True
rest = text[len(_SYSTEM_IDENTITY) :].lstrip("\n")
identity_entry = {k: v for k, v in entry.items() if k != "text"}
identity_entry["text"] = _SYSTEM_IDENTITY
kept.append(identity_entry)
if rest:
moved_texts.append(rest)
continue
if text:
moved_texts.append(text)
if not identity_seen:
kept.insert(0, {"type": "text", "text": _SYSTEM_IDENTITY})
# Billing header first (no cache_control — changes per request).
api_kwargs["system"] = [billing_entry] + kept
if moved_texts:
_prepend_to_first_user_message(messages, moved_texts)
_fix_temperature_for_oauth_adaptive(api_kwargs, site="build_kwargs")
# ---------------------------------------------------------------------------
# Monkey-patch installation
# ---------------------------------------------------------------------------
def _get_version_safely(aa_module: Any) -> str:
"""Return the Claude CLI version string from the adapter module."""
getter = getattr(aa_module, "_get_claude_code_version", None)
if callable(getter):
try:
version = getter()
if isinstance(version, str) and version and version[0].isdigit():
return version
except Exception:
pass
fallback = getattr(aa_module, "_CLAUDE_CODE_VERSION_FALLBACK", None)
if isinstance(fallback, str) and fallback:
return fallback
return "2.1.90"
def _install_aux_client_hook(force: bool = False) -> bool:
"""Patch the auxiliary client to strip temperature on OAuth adaptive models."""
try:
from agent import auxiliary_client as ac # type: ignore[import-not-found]
except Exception as exc:
logger.warning("aux_client_hook_failed_import: %s: %s", type(exc).__name__, exc)
sys.stderr.write(
f"[anthropic_billing_bypass] aux_client_hook_failed_import: "
f"{type(exc).__name__}: {exc}\n"
)
return False
adapter_cls = getattr(ac, "_AnthropicCompletionsAdapter", None)
if adapter_cls is None:
logger.warning("aux_client_hook_failed: _AnthropicCompletionsAdapter not found")
return False
if getattr(adapter_cls, "_AUX_CLIENT_TEMP_HOOK_APPLIED", False) and not force:
logger.debug("aux_client_hook already installed")
return True
original_create = getattr(adapter_cls, "create", None)
if not callable(original_create):
logger.warning("aux_client_hook_failed: create() not callable on adapter")
return False
def patched_create(self: Any, **kwargs: Any) -> Any:
real_client = getattr(self, "_client", None)
if real_client is None:
return original_create(self, **kwargs)
messages_obj = getattr(real_client, "messages", None)
if messages_obj is None:
return original_create(self, **kwargs)
is_oauth = bool(getattr(self, "_is_oauth", False))
if not is_oauth:
return original_create(self, **kwargs)
inner_original = messages_obj.create
def fixed_messages_create(**inner_kwargs: Any) -> Any:
try:
_fix_temperature_for_oauth_adaptive(inner_kwargs, site="aux_client")
except Exception as exc:
logger.warning(
"aux_client_hook: temperature fix raised %s: %s",
type(exc).__name__,
exc,
)
return inner_original(**inner_kwargs)
try:
messages_obj.create = fixed_messages_create
rebind_ok = True
except (AttributeError, TypeError):
rebind_ok = False
try:
if rebind_ok:
return original_create(self, **kwargs)
class _ShimMessages:
create = staticmethod(fixed_messages_create)
class _ShimClient:
messages = _ShimMessages()
self._client = _ShimClient()
try:
return original_create(self, **kwargs)
finally:
self._client = real_client
finally:
if rebind_ok:
try:
del messages_obj.create
except (AttributeError, TypeError):
messages_obj.create = inner_original
patched_create.__name__ = original_create.__name__
patched_create.__qualname__ = getattr(
original_create, "__qualname__", original_create.__name__
)
patched_create.__doc__ = original_create.__doc__
patched_create.__wrapped__ = original_create # type: ignore[attr-defined]
adapter_cls.create = patched_create
adapter_cls._AUX_CLIENT_TEMP_HOOK_APPLIED = True
logger.info(
"Aux client temperature hook installed on _AnthropicCompletionsAdapter.create"
)
sys.stderr.write(
"[anthropic_billing_bypass] Aux client temperature hook installed\n"
)
return True
def apply_patches(anthropic_adapter_module: Any = None) -> bool:
"""Install the bypass on ``agent.anthropic_adapter``.
Called by the sitecustomize hook after the module is imported. Returns
``True`` on success, ``False`` if the target module is incompatible.
Idempotent — safe to call multiple times.
"""
aa = anthropic_adapter_module
if aa is None:
try:
from agent import anthropic_adapter as aa # type: ignore[import-not-found,no-redef]
except ImportError as exc:
logger.warning("Cannot import agent.anthropic_adapter: %s", exc)
return False
if getattr(aa, "_CLAUDE_CODE_BYPASS_APPLIED", False):
logger.debug("Claude Code bypass already installed")
return True
# 1. Add the missing beta flag.
new_beta = "prompt-caching-scope-2026-01-05"
oauth_betas = getattr(aa, "_OAUTH_ONLY_BETAS", None)
if isinstance(oauth_betas, list) and new_beta not in oauth_betas:
oauth_betas.append(new_beta)
logger.info("Appended beta flag: %s", new_beta)
# 2. Verify the target function exists with the expected signature.
original_build = getattr(aa, "build_anthropic_kwargs", None)
if not callable(original_build):
logger.warning(
"agent.anthropic_adapter.build_anthropic_kwargs not found — "
"skipping monkey-patch (incompatible hermes-agent version?)"
)
return False
try:
sig = inspect.signature(original_build)
if "is_oauth" not in sig.parameters:
logger.warning(
"build_anthropic_kwargs lacks 'is_oauth' param — "
"skipping monkey-patch (incompatible hermes-agent version?)"
)
return False
except (TypeError, ValueError) as exc:
logger.warning("Cannot introspect build_anthropic_kwargs: %s", exc)
return False
# 3. Wrap build_anthropic_kwargs to apply the bypass on OAuth requests.
def patched_build_anthropic_kwargs(*args: Any, **kwargs: Any) -> Dict[str, Any]:
result = original_build(*args, **kwargs)
try:
bound = sig.bind_partial(*args, **kwargs)
bound.apply_defaults()
is_oauth = bool(bound.arguments.get("is_oauth", False))
except TypeError:
is_oauth = bool(kwargs.get("is_oauth", False))
if is_oauth and isinstance(result, dict):
try:
apply_claude_code_bypass(result, _get_version_safely(aa))
except Exception as exc:
logger.warning(
"apply_claude_code_bypass raised %s: %s",
type(exc).__name__,
exc,
)
traceback.print_exc(file=sys.stderr)
return result
patched_build_anthropic_kwargs.__name__ = original_build.__name__
patched_build_anthropic_kwargs.__qualname__ = getattr(
original_build, "__qualname__", original_build.__name__
)
patched_build_anthropic_kwargs.__doc__ = original_build.__doc__
patched_build_anthropic_kwargs.__module__ = getattr(
original_build, "__module__", __name__
)
patched_build_anthropic_kwargs.__wrapped__ = original_build # type: ignore[attr-defined]
aa.build_anthropic_kwargs = patched_build_anthropic_kwargs
aa._CLAUDE_CODE_BYPASS_APPLIED = True # type: ignore[attr-defined]
logger.info("Claude Code OAuth bypass installed (build_anthropic_kwargs)")
sys.stderr.write("[anthropic_billing_bypass] Claude Code OAuth bypass installed\n")
_install_aux_client_hook()
return True