Adds Client Secret Credentials Support

[peombwa]

This PR closes #1366 by adding -Credential parameter of type PSCredential to Connect-MgGraph command.

The parameter is being added to:

• Support the authentication scenarios mentioned in Add -Credential as authentification method to the Connect-MgGraph Command #1366.
• Align with MS Graph CLI as mentioned in Support client certificate login msgraph-cli#147 (comment).

Proposes Usage

[nkasco]

Won't this cause user confusion when users inevitably try to use -Credential within Connect-MgGraph for ROPC / User Credential auth flow use with delegated permission types? I get that you're only intending to add support for client secrets / App Only, I just think in the process it might be creating UX confusion.

Perhaps an alias or rename of the parameter could aleviate this. -ClientSecret, -ClientSecretCredential, -AppCredential, or -AppSecret might be a few possibilities.

#125 (comment) - Looks like it already has created some confusion unless I've completely misunderstood the code. Keep me honest here.

[grzegorzwierzbicki]

This is completely wrong and confusing
-Credential should accept username and password for accessing the application with delegated permissions.

#1366 and similar should not be closed as the expectation was to add support for non-interactive username/password login

[grzegorzwierzbicki]

On top of that, the v2 module no longer accepts tokens acquired with MSAL.PS
Why are you doing this ?
Why are you working so hard on making life miserable for anyone who just wants to use Graph in a script.

$AccessToken = Get-MsalToken -ClientId $PowerShellGraphAppID -TenantId $TenantId -UserCredential $creds -Scopes "User.ReadWrite.All"
Connect-MgGraph -AccessToken $AccessToken.AccessToken
Connect-MgGraph : Cannot bind parameter 'AccessToken'. Cannot convert the "eyJ....5bA" value of type "System.String" to type "System.Security.SecureString"

[nkasco]

On top of that, the v2 module no longer accepts tokens acquired with MSAL.PS

Why are you doing this ?

Why are you working so hard on making life miserable for anyone who just wants to use Graph in a script.

$AccessToken = Get-MsalToken -ClientId $PowerShellGraphAppID -TenantId $TenantId -UserCredential $creds -Scopes "User.ReadWrite.All"

Connect-MgGraph -AccessToken $AccessToken.AccessToken

Connect-MgGraph : Cannot bind parameter 'AccessToken'. Cannot convert the "eyJ....5bA" value of type "System.String" to type "System.Security.SecureString"

You need to convert the string token to secure string to use with the v2 module. That was documented in the breaking changes. MSAL.PS isn't broken.

That said, I do agree about the credentials parameter being confusing as I documented above.