apollo-core/src/main/java/com/ctrip/framework/foundation/internals/provider/DefaultApplicationProvider.java/DefaultApplicationProvider/initDeprecatedAccessKey
class DefaultApplicationProvider:  @SuppressWarnings("deprecation")
  private String initDeprecatedAccessKey() {
    // 1. Get ACCESS KEY SECRET from System Property
    String accessKeySecret = System
        .getProperty(ApolloClientSystemConsts.DEPRECATED_APOLLO_ACCESS_KEY_SECRET);
    if (!Utils.isBlank(accessKeySecret)) {
      accessKeySecret = accessKeySecret.trim();
      logger.info(
          "ACCESS KEY SECRET is set by apollo.accesskey.secret property from System Property");
      DeprecatedPropertyNotifyUtil
          .warn(ApolloClientSystemConsts.DEPRECATED_APOLLO_ACCESS_KEY_SECRET,
              ApolloClientSystemConsts.APOLLO_ACCESS_KEY_SECRET);
      return accessKeySecret;
    }

    //2. Try to get ACCESS KEY SECRET from OS environment variable
    accessKeySecret = System
        .getenv(ApolloClientSystemConsts.DEPRECATED_APOLLO_ACCESS_KEY_SECRET_ENVIRONMENT_VARIABLES);
    if (!Utils.isBlank(accessKeySecret)) {
      accessKeySecret = accessKeySecret.trim();
      logger.info(
          "ACCESS KEY SECRET is set by APOLLO_ACCESSKEY_SECRET property from OS environment variable");
      DeprecatedPropertyNotifyUtil
          .warn(ApolloClientSystemConsts.DEPRECATED_APOLLO_ACCESS_KEY_SECRET_ENVIRONMENT_VARIABLES,
              ApolloClientSystemConsts.APOLLO_ACCESS_KEY_SECRET_ENVIRONMENT_VARIABLES);
      return accessKeySecret;
    }

    // 3. Try to get ACCESS KEY SECRET from app.properties.
    accessKeySecret = m_appProperties
        .getProperty(ApolloClientSystemConsts.DEPRECATED_APOLLO_ACCESS_KEY_SECRET);
    if (!Utils.isBlank(accessKeySecret)) {
      accessKeySecret = accessKeySecret.trim();
      logger.info("ACCESS KEY SECRET is set by apollo.accesskey.secret property from {}",
          APP_PROPERTIES_CLASSPATH);
      DeprecatedPropertyNotifyUtil
          .warn(ApolloClientSystemConsts.DEPRECATED_APOLLO_ACCESS_KEY_SECRET,
              ApolloClientSystemConsts.APOLLO_ACCESS_KEY_SECRET);
      return accessKeySecret;
    }
    return null;
  }