Orfeo toolbox (OTB) algorithms in QGIS 3.0?

The OTB provider was removed from QGIS 3.0. See the QGIS 3.0.0 changelog: http://changelog.qgis.org/en/qgis/version/3.0.0/#removed-otb-lidartools-providers-from-processing

As long as nobody makes a QGIS plugin to add OTB as a processing provider, it isn't possible to use OTB in QGIS 3.0.

Here are some resources that may help,

1. https://www.sigterritoires.fr/index.php/en/add-orfeo-toolbox-to-qgis-3-x/

2. https://gitlab.orfeo-toolbox.org/orfeotoolbox/qgis-otb-plugin