Lazy load dependencies

[rayluo]

Lazy load MSAL's dependencies. This resolves #423.

Also remove an old workaround. P.S.: @xiangyan99, after this change, the Azure Identity 1.3.* and 1.4 versions are expected to throw this exception:

AttributeError: module 'msal.authority' has no attribute 'requests'

[xiangyan99]

LGTM

[jiasli]

Actually Azure CLI already lazily imports MSAL. The issue #423 is only a (possibly not appropriate) suggestion.

I am not sure how much this change will benefit other MSAL users, who use the default requests HTTP client. But yea, lazy import requests is certainly beneficial to users how choose to use their own HTTP client.

[rayluo]

Actually Azure CLI already lazily imports MSAL. The issue #423 is only a (possibly not appropriate) suggestion.

I am not sure how much this change will benefit other MSAL users, who use the default requests HTTP client. But yea, lazy import requests is certainly beneficial to users how choose to use their own HTTP client.

It turns out, lazy loading our dependencies makes MSAL easier to be used in some restricted environment. So, we will still ship this.

[jiasli]

Could you share more info about "restricted environment"? If requests is not required, perhaps we need to tweak

microsoft-authentication-library-for-python/setup.py

Line 75 in 636a58c

'requests>=2.0.0,<3',