[Feature Request] Enable apps to decide what to do when the L2 cache fails (Retry)

[jmprieur]

Is your feature request related to a problem? Please describe.
Today, when the L2 cache fails, an error is logged, but given the L1 cache was able to proceed, we don't re-throw (think of Redis cache connection error)

Describe the solution you'd like

Have a new property in the MsalDistributedTokenCacheAdapterOptions, so that the application can handle the failure ?

 /// <summary>
 /// Callback offered to the app to be notified when the L2 cache fails.
 /// This way the app is given the possibility to act on the L2 cache,
 /// for instance, in the case of Redis, to reconnect. This is left to the application as it's
 /// the only one that knows about the real implementation of the L2 cache.
 /// The handler should return <c>true</c> if the cache should try again the operation, and
 /// <c>false</c> otherwise. When <c>true</c> is passed and the retry fails, an exception
 /// will be thrown.
 /// </summary>
 public Func<Exception, bool>? OnL2CacheFailure {get;set;}

Here is an example of how this would be hooked from the Startup.cs:

services.Configure<MsalDistributedTokenCacheAdapterOptions>(options =>
{
options.L1CacheSizeLimit = 10 * 1024 * 1024; // 10 Mb
options.OnL2CacheFailure = (ex) =>
{
  if (ex is StackExchange.Redis.RedisConnectionException)
  {
    // Attempt to act on the redis cache if at all possible?
    // Put here your reconnected code
    return true; // Retry
  } 
  return false;  // Don't retry.
 };
});

Describe alternatives you've considered
We could also decide of the behavior when it fails again on retry (we could be silent instead of throwing)

[jmprieur]

Advice from Henrik:

• Look on stack overflow about the Redis connection issues; etc ..
• @henrik-me will make sure we have the right people to help

[jmprieur]

Re opening until it's released.

[jennyf19]

Included in 1.8.0 release