docs: add warning for encoded credential (#4182)

* chore(docs): add warning for encoded credential * chore: generalize comment * chore: generate libraries at Wed Oct 22 16:38:42 UTC 2025 * Revert "chore(docs): add warning for encoded credential" This reverts commit b28885f. * chore: move warning to ConnectionProperties * chore: generate libraries at Wed Oct 22 20:11:58 UTC 2025 * chore: add warning to CREDENTIALS_URL as well * chore: generate libraries at Wed Oct 22 21:05:13 UTC 2025 --------- Co-authored-by: cloud-java-bot <cloud-java-bot@google.com>

Author: diegomarquezp

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ConnectionProperties.java

@@ -261,7 +261,11 @@ public class ConnectionProperties {
  CREDENTIALS_PROPERTY_NAME,
  "The location of the credentials file to use for this connection. If neither this"
  + " property or encoded credentials are set, the connection will use the default"
- + " Google Cloud credentials for the runtime environment.",
+ + " Google Cloud credentials for the runtime environment. WARNING: Using this"
+ + " property without proper validation can expose the application to security risks."
+ + " It is intended for use with credentials from a trusted source only, as it could"
+ + " otherwise allow end-users to supply arbitrary credentials. For more information,"
+ + " seehttps://cloud.google.com/docs/authentication/client-libraries#external-credentials",
  DEFAULT_CREDENTIALS,
  StringValueConverter.INSTANCE,
  Context.STARTUP);
@@ -270,7 +274,11 @@ public class ConnectionProperties {
  ENCODED_CREDENTIALS_PROPERTY_NAME,
  "Base64-encoded credentials to use for this connection. If neither this property or a"
  + " credentials location are set, the connection will use the default Google Cloud"
- + " credentials for the runtime environment.",
+ + " credentials for the runtime environment. WARNING: Enabling this property without"
+ + " proper validation can expose the application to security risks. It is intended"
+ + " for use with credentials from a trusted source only, as it could otherwise allow"
+ + " end-users to supply arbitrary credentials. For more information, see"
+ + "https://cloud.google.com/docs/authentication/client-libraries#external-credentials",
  null,
  StringValueConverter.INSTANCE,
  Context.STARTUP);