Hi @Romanowicz, Marcin,
As of now there is no API in MS graph to fetch the SAML Verification certificates (optional), If you want this feature, please raise a feature request so that it can be considered and implemented further.
Feature Request:https://feedbackportal.microsoft.com/feedback/forum/ebe2edae-97d1-ec11-a7b5-0022481f3c80
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