A new parameter type for processing algorithms, QgsProcessingParameterAuthConfig, has been added, allowing selection from available authentication configurations (and creation of new ones).
It allows creation of processing algorithm which can fully take advantage of QGIS' mature authentication handling, avoiding the need to use insecure string parameters for users to input sensitive logon credentials.
QgsProcessingParameterAuthConfig parameters are evaluated using QgsProcessingAlgorithm.parameterAsString(), which returns the selected authentication configuration ID.