I have Microsoft Dynamics CRM 2016 On Premise and IFD Enabled On it. In this situation I can not connect plugin Registration to CRM. Even I can not connect with XRMtoolbox. My problem is what is Home Realm URL?
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The Problem is In adfs Endpoints. After you Install IFD on CRM You want a Important Endpoint That Named "Mex".
For Solve The Problem First go to ADFS Management and go to endpoints and Click on adfs/services/trust/Mex and click on Enable and Enable on proxy for this Endpoint. after that reset the iis and adfs service. Then You can Browse that enpoint with https://service.contoso.com/adfs/services/trust/mex. if you See the Metadata Xml Document Now You Can Connect With Any Tool Like Portal, Plugin Registration, Xrmtoolbox, etc. but If you Don't see this metadata use this Command in Power shell to Change The Adfs Port.
i Choose 809 for My Port And You Can choose any port you want Except 443 or 80 or 90, Then like before Restart The IIS and Restart ADFS Service and then you Can see metadata And You Can Connect With Any Application to CRM 2016 On Premise IFD Mode.
At The End Of this Answer You can See My Metadata Page And My Connected Plugin Registration Tool Pictures.
If You Have Any Question You Can Ask it From Me.