[Feature Request- Breaking change] Use an actual MemoryCache with eviction when instructed

[bgavrilMS]

Today, Id.Web configures MSAL to use SharedMemoryCache - a static cache. This is fast, but no eviction.

With the introduction of new concepts like FMI, which increase the number of tokens, a cache without eviction becomes problematic.

Design

Id.Web configured the static cache here:

microsoft-identity-web/src/Microsoft.Identity.Web.TokenAcquisition/TokenAcquisition.cs

Line 796 in 2b8fbf0

builder.WithCacheOptions(CacheOptions.EnableSharedCacheOptions);

when the user configures a MemoryCache, Id.Web forces use the static cache.

Instead, we should actually use cache adapter (i.e. delete the condition here

microsoft-identity-web/src/Microsoft.Identity.Web.TokenAcquisition/TokenAcquisition.cs

Line 849 in 2b8fbf0

if (!(_tokenCacheProvider is MsalMemoryTokenCacheProvider))

)

[jennyf19]

Please provide a spec or design. Thanks @bgavrilMS

[bgavrilMS]

Done, updated the original issue.