code: public Class<? extends AccessTokenProvider> getAccessTokenProviderClass(Configuration config) {
      return config.getClass(
          configPrefix + ACCESS_TOKEN_PROVIDER_IMPL_SUFFIX, null, AccessTokenProvider.class);
    }
docs: Get the class that implements the AccessTokenProvider, from Hadoop {@link Configuration}.
  
  @param config Hadoop {@link Configuration}
  @return the class object of the class that implements the AccessTokenProvider, null if there
  are no such classes.