docs: add warning against accepting untrusted credentials (#8045)

PiperOrigin-RevId: 719330114
Source-Link: googleapis/googleapis@9e0f143
Source-Link: https://github.com/googleapis/googleapis-gen/commit/9612bdf86cdb1a894859806f3395829f1cba4f1c
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src/V2/Client/TraceServiceClient.php

@@ -182,6 +182,12 @@ public static function parseName(string $formattedName, ?string $template = null
      *           {@see \Google\Auth\FetchAuthTokenInterface} object or
      *           {@see \Google\ApiCore\CredentialsWrapper} object. Note that when one of these
      *           objects are provided, any settings in $credentialsConfig will be ignored.
+     *           *Important*: If you accept a credential configuration (credential
+     *           JSON/File/Stream) from an external source for authentication to Google Cloud
+     *           Platform, you must validate it before providing it to any Google API or library.
+     *           Providing an unvalidated credential configuration to Google APIs can compromise
+     *           the security of your systems and data. For more information {@see
+     *           https://cloud.google.com/docs/authentication/external/externally-sourced-credentials}
      *     @type array $credentialsConfig
      *           Options used to configure credentials, including auth token caching, for the
      *           client. For a full list of supporting configuration options, see