[keycloak-user] standard vs implicit flow in SPA

[Marek Posolda]

On 01/04/16 02:21, Anthony Fryer wrote:
>
> Hi,
>
> Up until recently I automatically selected to use implicit grant flow 
> from SPAs, but lately I’ve been re-assessing this since the keycloak 
> javascript adapter provides standard flow out of the box and makes 
> that a viable option.  I also note that the keycloak admin console is 
> a HTML5/javascript/angular js app that uses the keycloak js adapter 
> and uses the standard flow.  As a side note I find the client defaults 
> interesting in that Implicit flow is disabled, but direct access 
> grants are enabled (I’m coming from a mitreid connect implementation 
> where direct access grants where disabled by default and implicit flow 
> was enabled, so just wonder what the thinking is behind this since 
> direct access grants are discouraged).
>
Direct grants is enabled mostly for backwards compatibility and for 
having slightly easier some admin tasks. For example because direct 
grant is enabled, you have possibility to invoke admin REST endpoints 
once you start Keycloak, which is widely used in tests. Without direct 
grants enabled, you would first need to manually go to admin console and 
enable it for admin console client, but that's not easily just with 
admin REST endpoints (outside admin console UI) if it is disabled - in 
other words it's classic chicken-egg problem.

The direct grants is discouraged mainly because it requires users to 
enter their password in your app instead of Keycloak server. However:
- If your app is web-based and doesn't require direct grants, you just 
won't ask users to enter their password into your app
- If your app is not web-based and requires direct grants, you would 
still need to enable direct grant and ask people to enter their password 
into your application. If they don't trust it, they just reject to enter 
password to your app.

So from security and end-users perspective, there is not much difference 
between the case when direct access grant is enabled or disabled by 
default IMO.
>
> I’m really wondering why are you pushing standard flow from the 
> keycloak javascript adapter instead of implicit?  What are the 
> benefits that make standard flow better in this case?  One thing I 
> have seen mentioned is refresh tokens obtained in standard flow make 
> it easy to get a new access token, but I thought you could get refresh 
> tokens from the implicit flow anyway, and even if not, if a user logs 
> in with “remember me”, then getting a new access token doesn’t require 
> re-entering credentials by the user.  I want to make sure that when 
> implementing keycloak in our SPA we choose the best flow and want to 
> know if there’s some reason standard flow is best.
>
Yes, the refreshing tokens is not allowed in implicit flow per OIDC 
specification. Also there are accessToken and idToken sent in the URI 
fragment in implicit flow, which can in theory have some security 
implications.

So with implicit flow, you have to redirect to login screen (as you 
mentioned above) instead of just simply refreshing tokens. Redirecting 
to login screen is usually worse for performance-wise than refreshing 
tokens and also requires some change in logic of your javascript app, 
but it's doable (For example you can implement callback 
keycloak.onTokenExpired or you can always manually check the expiration 
on accessToken before sending refresh request to 3rd party service). 
Logic for refreshing token in javascript app is quite simple, you just 
need to wrap the REST call with keycloak.update to ensure the 
accessToken is automatically refreshed by adapter in case that it's 
expired (or going to be expired).

Marek
>
> Regards,
>
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