code: @NonNull
      public static Map<String, Object> createRetrieveSourceParams(
              @NonNull @Size(min = 1) String clientSecret) {
          final Map<String, Object> params = new HashMap<>();
          params.put(API_PARAM_CLIENT_SECRET, clientSecret);
          return params;
      }
docs: Create parameters needed to retrieve a source.
  
  @param clientSecret the client secret for the source, needed because the Android SDK uses
  a public key
  @return a {@link Map} matching the parameter name to the client secret, ready to send to
  the server.