Fix OAuth2.0 based authentication examples problems using cookie

[nokazn]

Some examples using OAuth 2.0 based authentication with cookie doesn't work correctly in modern browser like Google Chrome and Firefox.
In these examples, state value are not set correctly in cookie because the requests for Cloud Functions are sent in cross domain and are not Top Level Navigation.
If SameSite attribute are not set, browsers treats it as Lax value by default. So I think SameSite attribute should be set to None.

Edit
The solution in #849 seems to be better, so the example in spotify-auth followed this.
State cookie is sent through the same domain and use __session key instead of state.
The examples of Instagram and Linkedin are fixed by #849, so I reverted modification for these examples.

[samtstern]

@nokazn thanks for this contribution! I don't know enough about browser cookies to review it but I hope @jhuleatt does.

[kevinguebert]

@nokazn I ran into the same issues with authentication (for spotify) and tried out this solution. When setting setting sameSite: 'none' I received this error that caused the function not to run:

TypeError: option sameSite is invalid
    at Object.serialize (/workspace/node_modules/cookie/index.js:174:15)
    at ServerResponse.res.cookie (/workspace/node_modules/express/lib/response.js:853:36) 

Changing it up to SameSite: 'none' with the first S uppercased solved the error. Have you seen that issue at all?

[nokazn]

@kevinguebert

Changing it up to SameSite: 'none' with the first S uppercased solved the error. Have you seen that issue at all?

I tried some times, but couldn't reproduce the above error in my environment.
I think it's a dependency problem. The version of cookie package which express in firebase-functions, or cooike-parser uses may be old. cookie@0.3.x cannot address sameSite: 'none' attribute.
You can also check here.

[mjroyappa]

why is sameSite: 'None' still not part of the latest sample? I was stuck on this for quite a while thinking my setup was wrong or something