Support dynamically updating the ServiceCertificates during rollover (ASP.NET Core)

[chwallen]

We are using rolling certificates with quite short validity periods (60 - 90 days). In order for the rollover to take effect in the metadata, we need to restart our service as the certificates are loaded once from disk during AddSaml2. If the Certificate property of ServiceCertificate was virtual, or the ServiceCertificateCollection would use IServiceCertificates instead, we could easily implement this in a subclass.

Environment:

• .NET Core 8
• Sustainsys.Saml2.AspNetCore2 v2.9.2

[AndersAbel]

Reopening and adding as a possible future feature to consider for v3.