Microsoft Teams Client API Example - Getting OAuth Bearer Token (https://blog.natfan.io/teams/1)

ms-teams-get-oauth.ps1

function Get-OAuthToken {
  [CmdletBinding()]
  [OutputType([string])]
  param (
    [Parameter(Mandatory)]
    [Parameter(Mandatory)][ValidateScript({[GUID]::TryParse($_, [ref][GUID]::Empty)})][String]$TenantID,
    [Parameter(Mandatory)][PSCredential][System.Management.Automation.CredentialAttribute()]$Credential
  )

  try {
    $Username = $Credential.Username
    $Password = $Credential.Password

    # Set Resource URI to Microsoft Teams OAuth API
    $resourceAppIDURI = 'https://api.spaces.skype.com'
    # Set Authority to Azure AD Tenant
    $Authority = 'https://login.microsoftonline.com/common/' + $TenantID
    $OAuthCredential = [Microsoft.IdentityModel.Clients.ActiveDirectory.UserPasswordCredential]::new($Username, $Password)
    $AuthContext = [Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext]::new($Authority)
    $Token = [Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContextIntegratedAuthExtensions]::AcquireTokenAsync($AuthContext, $ResourceAppIDURI, $PowerShellClientID, $OAuthCredential)
    $Token.Wait() # Wait for the async function to finish.
  } catch {
    throw $_
    $ErrorMessage = 'Failed to aquire OAuth token.'
    Write-Error -Message 'Failed to aquire OAuth token'
    break
  }
  return $Token
}