[Feature Request] [L] TokenCacheNotificationArgs should expose the token expiry so that cache can optimize eviction (client_credentials only)

Is your feature request related to a problem? Please describe. In token cache serializers for confidential client applications:

• for user flows, a RT is present in the cache and expiration cannot be determined, because tokens can be refreshed indefinitely.
• for AcquireTokenForClient however, there is no RT and the expiration of the cache can be computed as the max over the expiration of each access token in cache.

Describe the solution you’d like

In TokenCacheNotificationArgs add a new property of type SuggestedCacheExpiry, and of the same type as the expiry in the token cache times (I suppose this is DateTimeOffset, but this needs to be checked).

This property will be computed by items.Max(item => item.ExpiresOnUnixTimestamp), and then convert that to a UtcDateTime.

class TokenCacheNotificationArgs
{
 // Other members

 /// <Summary>
 /// Suggested value of the expiry, to help determining the cache eviction time. 
 // This value is <b>only</b> set on the <code>OnAfterAcces</code> delegate, on a cache write
 /// operation (that is when <code>args.HasStateChanged<code> is <code>true</code>) and when the cache write 
 /// is triggered from the <code>AcquireTokenForClient<code> method. In all other cases it's <code>null<code>, as there is a refresh token, and therefore the
 /// access tokens are refreshable.
 /// </Summary> 
 UtcDateTime? SuggestedCacheExpiry {get; private set;}

[jmprieur]

@bgavrilMS : yes it should be nullable, but I don’t think we have nullable in MSAL.NET? Yes, in the InAfterAccess, and probably only when (args.HasStateChanged) ?

[trwalke]

released in 4.34.0