273 lines
11 KiB
PHP
273 lines
11 KiB
PHP
<?php
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/*
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* Copyright 2024 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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namespace Google\Auth\CredentialSource;
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use Google\Auth\ExecutableHandler\ExecutableHandler;
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use Google\Auth\ExecutableHandler\ExecutableResponseError;
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use Google\Auth\ExternalAccountCredentialSourceInterface;
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use RuntimeException;
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/**
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* ExecutableSource enables the exchange of workload identity pool external credentials for
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* Google access tokens by retrieving 3rd party tokens through a user supplied executable. These
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* scripts/executables are completely independent of the Google Cloud Auth libraries. These
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* credentials plug into ADC and will call the specified executable to retrieve the 3rd party token
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* to be exchanged for a Google access token.
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*
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* To use these credentials, the GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES environment variable
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* must be set to '1'. This is for security reasons.
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*
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* Both OIDC and SAML are supported. The executable must adhere to a specific response format
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* defined below.
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*
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* The executable must print out the 3rd party token to STDOUT in JSON format. When an
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* output_file is specified in the credential configuration, the executable must also handle writing the
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* JSON response to this file.
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*
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* <pre>
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* OIDC response sample:
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* {
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* "version": 1,
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* "success": true,
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* "token_type": "urn:ietf:params:oauth:token-type:id_token",
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* "id_token": "HEADER.PAYLOAD.SIGNATURE",
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* "expiration_time": 1620433341
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* }
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*
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* SAML2 response sample:
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* {
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* "version": 1,
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* "success": true,
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* "token_type": "urn:ietf:params:oauth:token-type:saml2",
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* "saml_response": "...",
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* "expiration_time": 1620433341
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* }
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*
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* Error response sample:
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* {
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* "version": 1,
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* "success": false,
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* "code": "401",
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* "message": "Error message."
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* }
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* </pre>
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*
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* The "expiration_time" field in the JSON response is only required for successful
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* responses when an output file was specified in the credential configuration
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*
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* The auth libraries will populate certain environment variables that will be accessible by the
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* executable, such as: GOOGLE_EXTERNAL_ACCOUNT_AUDIENCE, GOOGLE_EXTERNAL_ACCOUNT_TOKEN_TYPE,
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* GOOGLE_EXTERNAL_ACCOUNT_INTERACTIVE, GOOGLE_EXTERNAL_ACCOUNT_IMPERSONATED_EMAIL, and
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* GOOGLE_EXTERNAL_ACCOUNT_OUTPUT_FILE.
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*/
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class ExecutableSource implements ExternalAccountCredentialSourceInterface
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{
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private const GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES = 'GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES';
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private const SAML_SUBJECT_TOKEN_TYPE = 'urn:ietf:params:oauth:token-type:saml2';
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private const OIDC_SUBJECT_TOKEN_TYPE1 = 'urn:ietf:params:oauth:token-type:id_token';
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private const OIDC_SUBJECT_TOKEN_TYPE2 = 'urn:ietf:params:oauth:token-type:jwt';
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private string $command;
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private ExecutableHandler $executableHandler;
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private ?string $outputFile;
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/**
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* @param string $command The string command to run to get the subject token.
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* @param string|null $outputFile
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*/
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public function __construct(
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string $command,
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?string $outputFile,
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?ExecutableHandler $executableHandler = null,
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) {
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$this->command = $command;
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$this->outputFile = $outputFile;
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$this->executableHandler = $executableHandler ?: new ExecutableHandler();
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}
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/**
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* Gets the unique key for caching
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* The format for the cache key is:
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* Command.OutputFile
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*
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* @return ?string
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*/
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public function getCacheKey(): ?string
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{
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return $this->command . '.' . $this->outputFile;
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}
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/**
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* @param callable|null $httpHandler unused.
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* @return string
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* @throws RuntimeException if the executable is not allowed to run.
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* @throws ExecutableResponseError if the executable response is invalid.
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*/
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public function fetchSubjectToken(?callable $httpHandler = null): string
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{
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// Check if the executable is allowed to run.
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if (getenv(self::GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES) !== '1') {
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throw new RuntimeException(
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'Pluggable Auth executables need to be explicitly allowed to run by '
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. 'setting the GOOGLE_EXTERNAL_ACCOUNT_ALLOW_EXECUTABLES environment '
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. 'Variable to 1.'
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);
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}
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if (!$executableResponse = $this->getCachedExecutableResponse()) {
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// Run the executable.
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$exitCode = ($this->executableHandler)($this->command);
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$output = $this->executableHandler->getOutput();
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// If the exit code is not 0, throw an exception with the output as the error details
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if ($exitCode !== 0) {
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throw new ExecutableResponseError(
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'The executable failed to run'
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. ($output ? ' with the following error: ' . $output : '.'),
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(string) $exitCode
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);
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}
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$executableResponse = $this->parseExecutableResponse($output);
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// Validate expiration.
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if (isset($executableResponse['expiration_time']) && time() >= $executableResponse['expiration_time']) {
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throw new ExecutableResponseError('Executable response is expired.');
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}
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}
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// Throw error when the request was unsuccessful
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if ($executableResponse['success'] === false) {
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throw new ExecutableResponseError($executableResponse['message'], (string) $executableResponse['code']);
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}
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// Return subject token field based on the token type
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return $executableResponse['token_type'] === self::SAML_SUBJECT_TOKEN_TYPE
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? $executableResponse['saml_response']
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: $executableResponse['id_token'];
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}
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/**
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* @return array<string, mixed>|null
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*/
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private function getCachedExecutableResponse(): ?array
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{
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if (
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$this->outputFile
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&& file_exists($this->outputFile)
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&& !empty(trim($outputFileContents = (string) file_get_contents($this->outputFile)))
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) {
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try {
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$executableResponse = $this->parseExecutableResponse($outputFileContents);
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} catch (ExecutableResponseError $e) {
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throw new ExecutableResponseError(
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'Error in output file: ' . $e->getMessage(),
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'INVALID_OUTPUT_FILE'
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);
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}
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if ($executableResponse['success'] === false) {
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// If the cached token was unsuccessful, run the executable to get a new one.
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return null;
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}
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if (isset($executableResponse['expiration_time']) && time() >= $executableResponse['expiration_time']) {
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// If the cached token is expired, run the executable to get a new one.
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return null;
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}
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return $executableResponse;
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}
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return null;
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}
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/**
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* @return array<string, mixed>
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*/
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private function parseExecutableResponse(string $response): array
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{
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$executableResponse = json_decode($response, true);
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if (json_last_error() !== JSON_ERROR_NONE) {
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throw new ExecutableResponseError(
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'The executable returned an invalid response: ' . $response,
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'INVALID_RESPONSE'
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);
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}
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if (!array_key_exists('version', $executableResponse)) {
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throw new ExecutableResponseError('Executable response must contain a "version" field.');
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}
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if (!array_key_exists('success', $executableResponse)) {
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throw new ExecutableResponseError('Executable response must contain a "success" field.');
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}
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// Validate required fields for a successful response.
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if ($executableResponse['success']) {
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// Validate token type field.
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$tokenTypes = [self::SAML_SUBJECT_TOKEN_TYPE, self::OIDC_SUBJECT_TOKEN_TYPE1, self::OIDC_SUBJECT_TOKEN_TYPE2];
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if (!isset($executableResponse['token_type'])) {
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throw new ExecutableResponseError(
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'Executable response must contain a "token_type" field when successful'
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);
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}
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if (!in_array($executableResponse['token_type'], $tokenTypes)) {
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throw new ExecutableResponseError(sprintf(
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'Executable response "token_type" field must be one of %s.',
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implode(', ', $tokenTypes)
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));
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}
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// Validate subject token for SAML and OIDC.
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if ($executableResponse['token_type'] === self::SAML_SUBJECT_TOKEN_TYPE) {
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if (empty($executableResponse['saml_response'])) {
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throw new ExecutableResponseError(sprintf(
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'Executable response must contain a "saml_response" field when token_type=%s.',
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self::SAML_SUBJECT_TOKEN_TYPE
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));
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}
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} elseif (empty($executableResponse['id_token'])) {
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throw new ExecutableResponseError(sprintf(
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'Executable response must contain a "id_token" field when '
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. 'token_type=%s.',
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$executableResponse['token_type']
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));
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}
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// Validate expiration exists when an output file is specified.
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if ($this->outputFile) {
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if (!isset($executableResponse['expiration_time'])) {
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throw new ExecutableResponseError(
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'The executable response must contain a "expiration_time" field for successful responses ' .
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'when an output_file has been specified in the configuration.'
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);
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}
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}
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} else {
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// Both code and message must be provided for unsuccessful responses.
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if (!array_key_exists('code', $executableResponse)) {
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throw new ExecutableResponseError('Executable response must contain a "code" field when unsuccessful.');
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}
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if (empty($executableResponse['message'])) {
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throw new ExecutableResponseError('Executable response must contain a "message" field when unsuccessful.');
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}
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}
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return $executableResponse;
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}
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}
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