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| 1 | +# Copyright 2025 Google LLC |
| 2 | +# |
| 3 | +# Licensed under the Apache License, Version 2.0 (the "License"); |
| 4 | +# you may not use this file except in compliance with the License. |
| 5 | +# You may obtain a copy of the License at |
| 6 | +# |
| 7 | +# http://www.apache.org/licenses/LICENSE-2.0 |
| 8 | +# |
| 9 | +# Unless required by applicable law or agreed to in writing, software |
| 10 | +# distributed under the License is distributed on an "AS IS" BASIS, |
| 11 | +# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 12 | +# See the License for the specific language governing permissions and |
| 13 | +# limitations under the License. |
| 14 | + |
| 15 | +"""Helpers for Agent Identity credentials.""" |
| 16 | + |
| 17 | +import base64 |
| 18 | +import hashlib |
| 19 | +import logging |
| 20 | +import os |
| 21 | +import re |
| 22 | +import time |
| 23 | +from urllib.parse import quote, urlparse |
| 24 | + |
| 25 | +from google.auth import environment_vars |
| 26 | +from google.auth import exceptions |
| 27 | +from google.auth.transport import _mtls_helper |
| 28 | + |
| 29 | + |
| 30 | +_LOGGER = logging.getLogger(__name__) |
| 31 | + |
| 32 | +CRYPTOGRAPHY_NOT_FOUND_ERROR = ( |
| 33 | + "The cryptography library is required for certificate-based authentication." |
| 34 | + "Please install it with `pip install google-auth[cryptography]`." |
| 35 | +) |
| 36 | + |
| 37 | +# SPIFFE trust domain patterns for Agent Identities. |
| 38 | +_AGENT_IDENTITY_SPIFFE_TRUST_DOMAIN_PATTERNS = [ |
| 39 | + r"^agents\.global\.org-\d+\.system\.id\.goog$", |
| 40 | + r"^agents\.global\.proj-\d+\.system\.id\.goog$", |
| 41 | +] |
| 42 | + |
| 43 | +_WELL_KNOWN_CERT_PATH = "/var/run/secrets/workload-spiffe-credentials/certificates.pem" |
| 44 | + |
| 45 | +# Constants for polling the certificate file. |
| 46 | +_FAST_POLL_CYCLES = 50 |
| 47 | +_FAST_POLL_INTERVAL = 0.1 # 100ms |
| 48 | +_SLOW_POLL_INTERVAL = 0.5 # 500ms |
| 49 | +_TOTAL_TIMEOUT = 30 # seconds |
| 50 | + |
| 51 | +# Calculate the number of slow poll cycles based on the total timeout. |
| 52 | +_SLOW_POLL_CYCLES = int( |
| 53 | + (_TOTAL_TIMEOUT - (_FAST_POLL_CYCLES * _FAST_POLL_INTERVAL)) / _SLOW_POLL_INTERVAL |
| 54 | +) |
| 55 | + |
| 56 | +_POLLING_INTERVALS = ([_FAST_POLL_INTERVAL] * _FAST_POLL_CYCLES) + ( |
| 57 | + [_SLOW_POLL_INTERVAL] * _SLOW_POLL_CYCLES |
| 58 | +) |
| 59 | + |
| 60 | + |
| 61 | +def _is_certificate_file_ready(path): |
| 62 | + """Checks if a file exists and is not empty.""" |
| 63 | + return path and os.path.exists(path) and os.path.getsize(path) > 0 |
| 64 | + |
| 65 | + |
| 66 | +def get_agent_identity_certificate_path(): |
| 67 | + """Gets the certificate path from the certificate config file. |
| 68 | +
|
| 69 | + The path to the certificate config file is read from the |
| 70 | + GOOGLE_API_CERTIFICATE_CONFIG environment variable. This function |
| 71 | + implements a retry mechanism to handle cases where the environment |
| 72 | + variable is set before the files are available on the filesystem. |
| 73 | +
|
| 74 | + Returns: |
| 75 | + str: The path to the leaf certificate file. |
| 76 | +
|
| 77 | + Raises: |
| 78 | + google.auth.exceptions.RefreshError: If the certificate config file |
| 79 | + or the certificate file cannot be found after retries. |
| 80 | + """ |
| 81 | + import json |
| 82 | + |
| 83 | + cert_config_path = os.environ.get(environment_vars.GOOGLE_API_CERTIFICATE_CONFIG) |
| 84 | + if not cert_config_path: |
| 85 | + return None |
| 86 | + |
| 87 | + has_logged_warning = False |
| 88 | + |
| 89 | + for interval in _POLLING_INTERVALS: |
| 90 | + try: |
| 91 | + with open(cert_config_path, "r") as f: |
| 92 | + cert_config = json.load(f) |
| 93 | + cert_path = ( |
| 94 | + cert_config.get("cert_configs", {}) |
| 95 | + .get("workload", {}) |
| 96 | + .get("cert_path") |
| 97 | + ) |
| 98 | + if _is_certificate_file_ready(cert_path): |
| 99 | + return cert_path |
| 100 | + except (IOError, ValueError, KeyError): |
| 101 | + if not has_logged_warning: |
| 102 | + _LOGGER.warning( |
| 103 | + "Certificate config file not found at %s (from %s environment " |
| 104 | + "variable). Retrying for up to %s seconds.", |
| 105 | + cert_config_path, |
| 106 | + environment_vars.GOOGLE_API_CERTIFICATE_CONFIG, |
| 107 | + _TOTAL_TIMEOUT, |
| 108 | + ) |
| 109 | + has_logged_warning = True |
| 110 | + pass |
| 111 | + |
| 112 | + # As a fallback, check the well-known certificate path. |
| 113 | + if _is_certificate_file_ready(_WELL_KNOWN_CERT_PATH): |
| 114 | + return _WELL_KNOWN_CERT_PATH |
| 115 | + |
| 116 | + # A sleep is required in two cases: |
| 117 | + # 1. The config file is not found (the except block). |
| 118 | + # 2. The config file is found, but the certificate is not yet available. |
| 119 | + # In both cases, we need to poll, so we sleep on every iteration |
| 120 | + # that doesn't return a certificate. |
| 121 | + time.sleep(interval) |
| 122 | + |
| 123 | + raise exceptions.RefreshError( |
| 124 | + "Certificate config or certificate file not found after multiple retries. " |
| 125 | + f"Token binding protection is failing. You can turn off this protection by setting " |
| 126 | + f"{environment_vars.GOOGLE_API_PREVENT_AGENT_TOKEN_SHARING_FOR_GCP_SERVICES} to false " |
| 127 | + "to fall back to unbound tokens." |
| 128 | + ) |
| 129 | + |
| 130 | + |
| 131 | +def get_and_parse_agent_identity_certificate(): |
| 132 | + """Gets and parses the agent identity certificate if not opted out. |
| 133 | +
|
| 134 | + Checks if the user has opted out of certificate-bound tokens. If not, |
| 135 | + it gets the certificate path, reads the file, and parses it. |
| 136 | +
|
| 137 | + Returns: |
| 138 | + The parsed certificate object if found and not opted out, otherwise None. |
| 139 | + """ |
| 140 | + # If the user has opted out of cert bound tokens, there is no need to |
| 141 | + # look up the certificate. |
| 142 | + is_opted_out = ( |
| 143 | + os.environ.get( |
| 144 | + environment_vars.GOOGLE_API_PREVENT_AGENT_TOKEN_SHARING_FOR_GCP_SERVICES, |
| 145 | + "true", |
| 146 | + ).lower() |
| 147 | + == "false" |
| 148 | + ) |
| 149 | + if is_opted_out: |
| 150 | + return None |
| 151 | + |
| 152 | + cert_path = get_agent_identity_certificate_path() |
| 153 | + if not cert_path: |
| 154 | + return None |
| 155 | + |
| 156 | + with open(cert_path, "rb") as cert_file: |
| 157 | + cert_bytes = cert_file.read() |
| 158 | + |
| 159 | + return parse_certificate(cert_bytes) |
| 160 | + |
| 161 | + |
| 162 | +def parse_certificate(cert_bytes): |
| 163 | + """Parses a PEM-encoded certificate. |
| 164 | +
|
| 165 | + Args: |
| 166 | + cert_bytes (bytes): The PEM-encoded certificate bytes. |
| 167 | +
|
| 168 | + Returns: |
| 169 | + cryptography.x509.Certificate: The parsed certificate object. |
| 170 | + """ |
| 171 | + try: |
| 172 | + from cryptography import x509 |
| 173 | + |
| 174 | + return x509.load_pem_x509_certificate(cert_bytes) |
| 175 | + except ImportError as e: |
| 176 | + raise ImportError(CRYPTOGRAPHY_NOT_FOUND_ERROR) from e |
| 177 | + |
| 178 | + |
| 179 | +def _is_agent_identity_certificate(cert): |
| 180 | + """Checks if a certificate is an Agent Identity certificate. |
| 181 | +
|
| 182 | + This is determined by checking the Subject Alternative Name (SAN) for a |
| 183 | + SPIFFE ID with a trust domain matching Agent Identity patterns. |
| 184 | +
|
| 185 | + Args: |
| 186 | + cert (cryptography.x509.Certificate): The parsed certificate object. |
| 187 | +
|
| 188 | + Returns: |
| 189 | + bool: True if the certificate is an Agent Identity certificate, |
| 190 | + False otherwise. |
| 191 | + """ |
| 192 | + try: |
| 193 | + from cryptography import x509 |
| 194 | + from cryptography.x509.oid import ExtensionOID |
| 195 | + |
| 196 | + try: |
| 197 | + ext = cert.extensions.get_extension_for_oid( |
| 198 | + ExtensionOID.SUBJECT_ALTERNATIVE_NAME |
| 199 | + ) |
| 200 | + except x509.ExtensionNotFound: |
| 201 | + return False |
| 202 | + uris = ext.value.get_values_for_type(x509.UniformResourceIdentifier) |
| 203 | + |
| 204 | + for uri in uris: |
| 205 | + parsed_uri = urlparse(uri) |
| 206 | + if parsed_uri.scheme == "spiffe": |
| 207 | + trust_domain = parsed_uri.netloc |
| 208 | + for pattern in _AGENT_IDENTITY_SPIFFE_TRUST_DOMAIN_PATTERNS: |
| 209 | + if re.match(pattern, trust_domain): |
| 210 | + return True |
| 211 | + return False |
| 212 | + except ImportError as e: |
| 213 | + raise ImportError(CRYPTOGRAPHY_NOT_FOUND_ERROR) from e |
| 214 | + |
| 215 | + |
| 216 | +def calculate_certificate_fingerprint(cert): |
| 217 | + """Calculates the URL-encoded, unpadded, base64-encoded SHA256 hash of a |
| 218 | + DER-encoded certificate. |
| 219 | +
|
| 220 | + Args: |
| 221 | + cert (cryptography.x509.Certificate): The parsed certificate object. |
| 222 | +
|
| 223 | + Returns: |
| 224 | + str: The URL-encoded, unpadded, base64-encoded SHA256 fingerprint. |
| 225 | + """ |
| 226 | + try: |
| 227 | + from cryptography.hazmat.primitives import serialization |
| 228 | + |
| 229 | + der_cert = cert.public_bytes(serialization.Encoding.DER) |
| 230 | + fingerprint = hashlib.sha256(der_cert).digest() |
| 231 | + # The certificate fingerprint is generated in two steps to align with GFE's |
| 232 | + # expectations and ensure proper URL transmission: |
| 233 | + # 1. Standard base64 encoding is applied, and padding ('=') is removed. |
| 234 | + # 2. The resulting string is then URL-encoded to handle special characters |
| 235 | + # ('+', '/') that would otherwise be misinterpreted in URL parameters. |
| 236 | + base64_fingerprint = base64.b64encode(fingerprint).decode("utf-8") |
| 237 | + unpadded_base64_fingerprint = base64_fingerprint.rstrip("=") |
| 238 | + return quote(unpadded_base64_fingerprint) |
| 239 | + except ImportError as e: |
| 240 | + raise ImportError(CRYPTOGRAPHY_NOT_FOUND_ERROR) from e |
| 241 | + |
| 242 | + |
| 243 | +def should_request_bound_token(cert): |
| 244 | + """Determines if a bound token should be requested. |
| 245 | +
|
| 246 | + This is based on the GOOGLE_API_PREVENT_AGENT_TOKEN_SHARING_FOR_GCP_SERVICES |
| 247 | + environment variable and whether the certificate is an agent identity cert. |
| 248 | +
|
| 249 | + Args: |
| 250 | + cert (cryptography.x509.Certificate): The parsed certificate object. |
| 251 | +
|
| 252 | + Returns: |
| 253 | + bool: True if a bound token should be requested, False otherwise. |
| 254 | + """ |
| 255 | + is_agent_cert = _is_agent_identity_certificate(cert) |
| 256 | + is_opted_in = ( |
| 257 | + os.environ.get( |
| 258 | + environment_vars.GOOGLE_API_PREVENT_AGENT_TOKEN_SHARING_FOR_GCP_SERVICES, |
| 259 | + "true", |
| 260 | + ).lower() |
| 261 | + == "true" |
| 262 | + ) |
| 263 | + return is_agent_cert and is_opted_in |
| 264 | + |
| 265 | + |
| 266 | +def call_client_cert_callback(): |
| 267 | + """Calls the client cert callback and returns the certificate and key.""" |
| 268 | + _, cert_bytes, key_bytes, passphrase = _mtls_helper.get_client_ssl_credentials( |
| 269 | + generate_encrypted_key=True |
| 270 | + ) |
| 271 | + return cert_bytes, key_bytes |
| 272 | + |
| 273 | + |
| 274 | +def get_cached_cert_fingerprint(cached_cert): |
| 275 | + """Returns the fingerprint of the cached certificate.""" |
| 276 | + if cached_cert: |
| 277 | + cert_obj = parse_certificate(cached_cert) |
| 278 | + cached_cert_fingerprint = calculate_certificate_fingerprint(cert_obj) |
| 279 | + else: |
| 280 | + raise ValueError("mTLS connection is not configured.") |
| 281 | + return cached_cert_fingerprint |
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