Change Hybrid Flow to Authorization Code Flow and add PKCE support

[vruello]

Hello,

Thanks for this repository which has been a time saver for me!

I had to implement an Authorization Code Flow client on Ionic - as recommended by IETF, so I used this repository and I changed some details.

I also got the code verifier from #7 and I put it in the sources to implement PKCE.

I don't know if you want to do the change from Hybrid to Authorization code flow, so be free to accept or not this PR. Perhaps it could be merged in another branch so we keep both flows.

[chougaard]

I'll look into it, but I don't have the time today :) Will get back to you.

[pliolis]

Hello, Does The auto refresh token mechanism is implimented ot not?

[vruello]

Hi @pliolis! As far as I know, it's not. A token refresh function is implemented, but you have to call it yourself, by writing an interceptor for example.

[pliolis]

Thank you my friend.