apollo-core/src/main/java/com/ctrip/framework/foundation/internals/provider/DefaultApplicationProvider.java/DefaultApplicationProvider/initAccessKey
class DefaultApplicationProvider:  private void initAccessKey() {
    // 1. Get ACCESS KEY SECRET from System Property
    accessKeySecret = System.getProperty(ApolloClientSystemConsts.APOLLO_ACCESS_KEY_SECRET);
    if (!Utils.isBlank(accessKeySecret)) {
      accessKeySecret = accessKeySecret.trim();
      logger
          .info("ACCESS KEY SECRET is set by apollo.access-key.secret property from System Property");
      return;
    }

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

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

    // 4. Try to get ACCESS KEY SECRET from deprecated config.
    accessKeySecret = initDeprecatedAccessKey();
    if (!Utils.isBlank(accessKeySecret)) {
      return;
    }
    accessKeySecret = null;
  }