I'm developing a smart home skill and using LWA for the account linking. I respond to the Alexa.Authorization AcceptGrant directive successfully after getting an access token from LWA. At this point I store the access and refresh tokens issued by LWA, associating it with the BearerToken from grantee section of the same request based on this documentation. Afterwards I can use the access token just fine by looking up the BearerToken from the endpoint.scope.token section of the Alexa directive.
While this works for a while (I can post events using the access token), at some point the Alexa directives start using a new BearerToken value for the same user in the endpoint.scope.token section at which point I can't associate them with an access token previously issued from LWA.
My question is how should I be tracking when the BearerToken in endpoint.scope.token changes? I can't seem to find any documentation or mention of when it rotates and how I'm supposed to track it or how I'm supposed to associate the requests with an access token once this value has changed.