To enable the new logon mechanism you have to change your web.config in the following way:

(1) disable forms auth by commenting it out:

    <authentication mode="Forms">
      <forms name="MyFormsAuthCookie" timeout="1440" slidingExpiration="true" loginUrl="Logon.aspx" ticketCompatibilityMode="Framework40"/>

(2) enable AD FS OIDC support by specifying an AdFsServer:

Given that you have the following AD FS configuration...

and the following AD FS Application Group for DPE...

The DPE web.config would look like...

<add key="AdFsServer" value=""/>

<add key="ida:AdfsMetadataEndpoint" value="" />
<add key="ida:Audience" value="microsoft:identityserver:jsDPE" />
<add key="ida:Issuer" value="" />

(3) enable WCF service support for OIDC by adding oidcEndpoint behavior extension and reference it in <behavior name="cors">:

        <behavior name="cors">
        <add name="oidcEndpoint" type="David.Dpe.Wcf.OidcEndpointBehaviorElement, David.Dpe.Wcf"/>