Add the ability to Refresh Auth Token Credentials

[vkagamlyk]

Add the ability to Refresh Auth Token Credentials

Currently when credentials expire, driver will continue trying to connect with the outdated credentials. There is no ability to update or refresh login credentials (See neo4j#834).

This PR introduces the ability to pass an optional credentials_refresher function to an authToken object which will change credentials as they become obsolete.

There are no breaking changes introduced in this PR.

There is a test which uses a simple credentials_refresher to validate that these modifications do not break serialization.

Intended use

auth_token = basic_auth("some_login", "ignored")
auth_token.add_credentials_refresher(credentials_refresher)
self.driver = GraphDatabase.driver(uri, auth=auth_token, encrypted=True)

I'm a first-time contributor and have just signed the CLA

[Cole-Greer]

LGTM. I think it it a bit clearer if that last sentence is rearranged to something like "There is a test which uses a simple credentials_refresher to validate that these modifications do not break serialization."

[kenhuuu]

LGTM

[xiazcy]

LGTM

[vkagamlyk]

opened as neo4j#891