refactor candid ui auth

[chenyan-dfinity]

• Allow customizing II url and derivationOrigin via parameter ii and origin. Report error on the login button if there is an error in the parameters.
• Remove derivationOrigin by default, unless in the mainnet and we can detect the destination canister has set candid UI to be the alternativeOrigin.

[frederikrothenberger]

if there is an easy way to detect that alternativeOrigin has been set in the destination canister, we can enable derivationOrigin without the parameter.

There is not, unfortunately.

[chenyan-dfinity]

There is not, unfortunately.

@frederikrothenberger Would it work if we fetch canister-id.icp0.io/.well-known/ii-alternative-origins, and parse the JSON response?

[rvanasa]

LGTM (suggested a fix for a subtle corner case).

[chenyan-dfinity]

cc @Web3NL

[frederikrothenberger]

There is not, unfortunately.

@frederikrothenberger Would it work if we fetch canister-id.icp0.io/.well-known/ii-alternative-origins, and parse the JSON response?

Yes, you can parse that file. And if it contains the URL of the candid UI then you could set the canister base URL as a derivationOrigin.

But this only works in a narrow scenario and should still be a user choice.

Even better would be, to allow checking an arbitrary domain (i.e. a new input field) where you look up the asset .well-known/ii-alternative-origins and if the candid UI is in the list, you use that domain as derivation origin. This way, the candid UI would also play nice with dapps hosted on custom domains.

[chenyan-dfinity]

Make sense. Users can still customize the derivation url with the origin parameter. This sounds like a good default option.