|
| 1 | +<?php |
| 2 | +/* |
| 3 | + * Copyright 2024 Google Inc. |
| 4 | + * |
| 5 | + * Licensed under the Apache License, Version 2.0 (the "License"); |
| 6 | + * you may not use this file except in compliance with the License. |
| 7 | + * You may obtain a copy of the License at |
| 8 | + * |
| 9 | + * http://www.apache.org/licenses/LICENSE-2.0 |
| 10 | + * |
| 11 | + * Unless required by applicable law or agreed to in writing, software |
| 12 | + * distributed under the License is distributed on an "AS IS" BASIS, |
| 13 | + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 | + * See the License for the specific language governing permissions and |
| 15 | + * limitations under the License. |
| 16 | + */ |
| 17 | + |
| 18 | +namespace Google\Auth\CredentialSource; |
| 19 | + |
| 20 | +use Google\Auth\ExecutableHandler\ExecutableHandler; |
| 21 | +use Google\Auth\ExecutableHandler\ExecutableResponseError; |
| 22 | +use Google\Auth\ExternalAccountCredentialSourceInterface; |
| 23 | +use RuntimeException; |
| 24 | + |
| 25 | +/** |
| 26 | + * ExecutableSource enables the exchange of workload identity pool external credentials for |
| 27 | + * Google access tokens by retrieving 3rd party tokens through a user supplied executable. These |
| 28 | + * scripts/executables are completely independent of the Google Cloud Auth libraries. These |
| 29 | + * credentials plug into ADC and will call the specified executable to retrieve the 3rd party token |
| 30 | + * to be exchanged for a Google access token. |
| 31 | + * |
| 32 | + * To use these credentials, the GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES environment variable |
| 33 | + * must be set to '1'. This is for security reasons. |
| 34 | + * |
| 35 | + * Both OIDC and SAML are supported. The executable must adhere to a specific response format |
| 36 | + * defined below. |
| 37 | + * |
| 38 | + * The executable must print out the 3rd party token to STDOUT in JSON format. When an |
| 39 | + * output_file is specified in the credential configuration, the executable must also handle writing the |
| 40 | + * JSON response to this file. |
| 41 | + * |
| 42 | + * <pre> |
| 43 | + * OIDC response sample: |
| 44 | + * { |
| 45 | + * "version": 1, |
| 46 | + * "success": true, |
| 47 | + * "token_type": "urn:ietf:params:oauth:token-type:id_token", |
| 48 | + * "id_token": "HEADER.PAYLOAD.SIGNATURE", |
| 49 | + * "expiration_time": 1620433341 |
| 50 | + * } |
| 51 | + * |
| 52 | + * SAML2 response sample: |
| 53 | + * { |
| 54 | + * "version": 1, |
| 55 | + * "success": true, |
| 56 | + * "token_type": "urn:ietf:params:oauth:token-type:saml2", |
| 57 | + * "saml_response": "...", |
| 58 | + * "expiration_time": 1620433341 |
| 59 | + * } |
| 60 | + * |
| 61 | + * Error response sample: |
| 62 | + * { |
| 63 | + * "version": 1, |
| 64 | + * "success": false, |
| 65 | + * "code": "401", |
| 66 | + * "message": "Error message." |
| 67 | + * } |
| 68 | + * </pre> |
| 69 | + * |
| 70 | + * The "expiration_time" field in the JSON response is only required for successful |
| 71 | + * responses when an output file was specified in the credential configuration |
| 72 | + * |
| 73 | + * The auth libraries will populate certain environment variables that will be accessible by the |
| 74 | + * executable, such as: GOOGLE_EXTERNAL_ACCOUNT_AUDIENCE, GOOGLE_EXTERNAL_ACCOUNT_TOKEN_TYPE, |
| 75 | + * GOOGLE_EXTERNAL_ACCOUNT_INTERACTIVE, GOOGLE_EXTERNAL_ACCOUNT_IMPERSONATED_EMAIL, and |
| 76 | + * GOOGLE_EXTERNAL_ACCOUNT_OUTPUT_FILE. |
| 77 | + */ |
| 78 | +class ExecutableSource implements ExternalAccountCredentialSourceInterface |
| 79 | +{ |
| 80 | + private const GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES = 'GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES'; |
| 81 | + private const SAML_SUBJECT_TOKEN_TYPE = 'urn:ietf:params:oauth:token-type:saml2'; |
| 82 | + private const OIDC_SUBJECT_TOKEN_TYPE1 = 'urn:ietf:params:oauth:token-type:id_token'; |
| 83 | + private const OIDC_SUBJECT_TOKEN_TYPE2 = 'urn:ietf:params:oauth:token-type:jwt'; |
| 84 | + |
| 85 | + private string $command; |
| 86 | + private ExecutableHandler $executableHandler; |
| 87 | + private ?string $outputFile; |
| 88 | + |
| 89 | + /** |
| 90 | + * @param string $command The string command to run to get the subject token. |
| 91 | + * @param string $outputFile |
| 92 | + */ |
| 93 | + public function __construct( |
| 94 | + string $command, |
| 95 | + ?string $outputFile, |
| 96 | + ExecutableHandler $executableHandler = null, |
| 97 | + ) { |
| 98 | + $this->command = $command; |
| 99 | + $this->outputFile = $outputFile; |
| 100 | + $this->executableHandler = $executableHandler ?: new ExecutableHandler(); |
| 101 | + } |
| 102 | + |
| 103 | + /** |
| 104 | + * @param callable $httpHandler unused. |
| 105 | + * @return string |
| 106 | + * @throws RuntimeException if the executable is not allowed to run. |
| 107 | + * @throws ExecutableResponseError if the executable response is invalid. |
| 108 | + */ |
| 109 | + public function fetchSubjectToken(callable $httpHandler = null): string |
| 110 | + { |
| 111 | + // Check if the executable is allowed to run. |
| 112 | + if (getenv(self::GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES) !== '1') { |
| 113 | + throw new RuntimeException( |
| 114 | + 'Pluggable Auth executables need to be explicitly allowed to run by ' |
| 115 | + . 'setting the GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES environment ' |
| 116 | + . 'Variable to 1.' |
| 117 | + ); |
| 118 | + } |
| 119 | + |
| 120 | + if (!$executableResponse = $this->getCachedExecutableResponse()) { |
| 121 | + // Run the executable. |
| 122 | + $exitCode = ($this->executableHandler)($this->command); |
| 123 | + $output = $this->executableHandler->getOutput(); |
| 124 | + |
| 125 | + // If the exit code is not 0, throw an exception with the output as the error details |
| 126 | + if ($exitCode !== 0) { |
| 127 | + throw new ExecutableResponseError( |
| 128 | + 'The executable failed to run' |
| 129 | + . ($output ? ' with the following error: ' . $output : '.'), |
| 130 | + (string) $exitCode |
| 131 | + ); |
| 132 | + } |
| 133 | + |
| 134 | + $executableResponse = $this->parseExecutableResponse($output); |
| 135 | + |
| 136 | + // Validate expiration. |
| 137 | + if (isset($executableResponse['expiration_time']) && time() >= $executableResponse['expiration_time']) { |
| 138 | + throw new ExecutableResponseError('Executable response is expired.'); |
| 139 | + } |
| 140 | + } |
| 141 | + |
| 142 | + // Throw error when the request was unsuccessful |
| 143 | + if ($executableResponse['success'] === false) { |
| 144 | + throw new ExecutableResponseError($executableResponse['message'], (string) $executableResponse['code']); |
| 145 | + } |
| 146 | + |
| 147 | + // Return subject token field based on the token type |
| 148 | + return $executableResponse['token_type'] === self::SAML_SUBJECT_TOKEN_TYPE |
| 149 | + ? $executableResponse['saml_response'] |
| 150 | + : $executableResponse['id_token']; |
| 151 | + } |
| 152 | + |
| 153 | + /** |
| 154 | + * @return array<string, mixed>|null |
| 155 | + */ |
| 156 | + private function getCachedExecutableResponse(): ?array |
| 157 | + { |
| 158 | + if ( |
| 159 | + $this->outputFile |
| 160 | + && file_exists($this->outputFile) |
| 161 | + && !empty(trim($outputFileContents = (string) file_get_contents($this->outputFile))) |
| 162 | + ) { |
| 163 | + try { |
| 164 | + $executableResponse = $this->parseExecutableResponse($outputFileContents); |
| 165 | + } catch (ExecutableResponseError $e) { |
| 166 | + throw new ExecutableResponseError( |
| 167 | + 'Error in output file: ' . $e->getMessage(), |
| 168 | + 'INVALID_OUTPUT_FILE' |
| 169 | + ); |
| 170 | + } |
| 171 | + |
| 172 | + if ($executableResponse['success'] === false) { |
| 173 | + // If the cached token was unsuccessful, run the executable to get a new one. |
| 174 | + return null; |
| 175 | + } |
| 176 | + |
| 177 | + if (isset($executableResponse['expiration_time']) && time() >= $executableResponse['expiration_time']) { |
| 178 | + // If the cached token is expired, run the executable to get a new one. |
| 179 | + return null; |
| 180 | + } |
| 181 | + |
| 182 | + return $executableResponse; |
| 183 | + } |
| 184 | + |
| 185 | + return null; |
| 186 | + } |
| 187 | + |
| 188 | + /** |
| 189 | + * @return array<string, mixed> |
| 190 | + */ |
| 191 | + private function parseExecutableResponse(string $response): array |
| 192 | + { |
| 193 | + $executableResponse = json_decode($response, true); |
| 194 | + if (json_last_error() !== JSON_ERROR_NONE) { |
| 195 | + throw new ExecutableResponseError( |
| 196 | + 'The executable returned an invalid response: ' . $response, |
| 197 | + 'INVALID_RESPONSE' |
| 198 | + ); |
| 199 | + } |
| 200 | + if (!array_key_exists('version', $executableResponse)) { |
| 201 | + throw new ExecutableResponseError('Executable response must contain a "version" field.'); |
| 202 | + } |
| 203 | + if (!array_key_exists('success', $executableResponse)) { |
| 204 | + throw new ExecutableResponseError('Executable response must contain a "success" field.'); |
| 205 | + } |
| 206 | + |
| 207 | + // Validate required fields for a successful response. |
| 208 | + if ($executableResponse['success']) { |
| 209 | + // Validate token type field. |
| 210 | + $tokenTypes = [self::SAML_SUBJECT_TOKEN_TYPE, self::OIDC_SUBJECT_TOKEN_TYPE1, self::OIDC_SUBJECT_TOKEN_TYPE2]; |
| 211 | + if (!isset($executableResponse['token_type'])) { |
| 212 | + throw new ExecutableResponseError( |
| 213 | + 'Executable response must contain a "token_type" field when successful' |
| 214 | + ); |
| 215 | + } |
| 216 | + if (!in_array($executableResponse['token_type'], $tokenTypes)) { |
| 217 | + throw new ExecutableResponseError(sprintf( |
| 218 | + 'Executable response "token_type" field must be one of %s.', |
| 219 | + implode(', ', $tokenTypes) |
| 220 | + )); |
| 221 | + } |
| 222 | + |
| 223 | + // Validate subject token for SAML and OIDC. |
| 224 | + if ($executableResponse['token_type'] === self::SAML_SUBJECT_TOKEN_TYPE) { |
| 225 | + if (empty($executableResponse['saml_response'])) { |
| 226 | + throw new ExecutableResponseError(sprintf( |
| 227 | + 'Executable response must contain a "saml_response" field when token_type=%s.', |
| 228 | + self::SAML_SUBJECT_TOKEN_TYPE |
| 229 | + )); |
| 230 | + } |
| 231 | + } elseif (empty($executableResponse['id_token'])) { |
| 232 | + throw new ExecutableResponseError(sprintf( |
| 233 | + 'Executable response must contain a "id_token" field when ' |
| 234 | + . 'token_type=%s.', |
| 235 | + $executableResponse['token_type'] |
| 236 | + )); |
| 237 | + } |
| 238 | + |
| 239 | + // Validate expiration exists when an output file is specified. |
| 240 | + if ($this->outputFile) { |
| 241 | + if (!isset($executableResponse['expiration_time'])) { |
| 242 | + throw new ExecutableResponseError( |
| 243 | + 'The executable response must contain a "expiration_time" field for successful responses ' . |
| 244 | + 'when an output_file has been specified in the configuration.' |
| 245 | + ); |
| 246 | + } |
| 247 | + } |
| 248 | + } else { |
| 249 | + // Both code and message must be provided for unsuccessful responses. |
| 250 | + if (!array_key_exists('code', $executableResponse)) { |
| 251 | + throw new ExecutableResponseError('Executable response must contain a "code" field when unsuccessful.'); |
| 252 | + } |
| 253 | + if (empty($executableResponse['message'])) { |
| 254 | + throw new ExecutableResponseError('Executable response must contain a "message" field when unsuccessful.'); |
| 255 | + } |
| 256 | + } |
| 257 | + |
| 258 | + return $executableResponse; |
| 259 | + } |
| 260 | +} |
0 commit comments