@azure/identity-TokenCredential

[nikithauc]

1. Introduces TokenCredentialAuthenticationProvider option so that authentication can be done using the @azure/identity- tokenCredential classes.
2. Added samples illustration the use of TokenCredentialAuthenticationProvider using AuthenticationCodeFlow and ClientCredentialFlow
3. Added and updated documents.
4. Introducing the authentication subfolder in src/ changing the structure of the source folders.
5. Added authProviderOptions/ folder which exports the msal and TokenCredential authentication provider options. This is done so that the we can use import {TokenCredentialAuthenticationProvider} from@microsoft/microsoft-graph-client/authProviders/azureTokenCredentials. This is a workaround for the limitations Recommendation for exposing multiple TypeScript modules from single NPM package microsoft/TypeScript#8305 ,
   Support for NodeJS 12.7+ package exports microsoft/TypeScript#33079.

The idea for using a submodule structure to export the authProviderOptions is because -

1. We are not exporting TokenCredentialAuthenticationProvider and ImplicitMsalAuthenticationProvider in the src/index.ts. This makes msal and @azure/identity an optional dependency for the user of the sdk. Marking them as option using peerDependenciesMeta.

2. ImplicitMSALAuthenticationProvider is not exported in index.js #230 - ImplicitMsalAuthenticationProvider was not exported in JS SDK version < 2.1 as using msal was optional but exporting in the index file would make msal a runtime dependency.

3. To import TokenCredentialAuthenticationProvider and ImplicitMsalAuthenticationProvider, the paths would be

    const {TokenCredentialAuthenticationProvider} = require("@microsoft/microsoft-graph- 
    client/authProviders/azureTokenCredentials");
    
    const{ImplicitMSALAuthenticationProvider}  = require("@microsoft/microsoft-graph-client/authProviders/msal");
   

4. Added tsconfig-sub-x.json to build the project using TypeScript Project References

[nikithauc]

This PR depends on #370

[ddyett]

may also be good to have a pure javascript sample at some point

[zengin]

Sorry for nitpicking on the typos. I added those comments as most of them appear in public documentation (MD files).

[nikithauc]

Sorry for nitpicking on the typos. I added those comments as most of them appear in public documentation (MD files).

Thanks for point those out. I should be careful about that.

[nikithauc]

may also be good to have a pure javascript sample at some point

Added.

[Stono]

Hey folks
I'm wondering if you have an ETA on 3.0.0 as I need this PR :)
Thanks