I don't think you can set it to never expire but you could certainly set a longer AccessTokenExpireTimeSpan
:
OAuthOptions = new OAuthAuthorizationServerOptions
{
TokenEndpointPath = new PathString("/Token"),
Provider = new ApplicationOAuthProvider(PublicClientId, UserManagerFactory),
AuthorizeEndpointPath = new PathString("/api/Account/ExternalLogin"),
AccessTokenExpireTimeSpan = TimeSpan.FromDays(14),
AllowInsecureHttp = true
};
app.UseOAuthBearerTokens(OAuthOptions);