$url = "https://example.sharepoint.com/"
$username="JohnDoe@example.com "
$password="Password"


$ie = New-Object -com internetexplorer.application;
$ie.visible = $true;
$ie.navigate($url);


while ($ie.Busy -eq $true)
{
    Start-Sleep -Milliseconds 1000;
}
$ie.Document.getElementById("login").value = $username
$ie.Document.getElementByID("Passwd").value=$password
$ie.Document.getElementById("cred_sign_in_button").Click();

<span id="cred_sign_in_button" tabindex="11" onclick="Post.SubmitCreds();return false;"
            class="button normaltext cred_sign_in_button refresh_domain_state" role="button">Sign in</span>
                    <div id="recover_container" class="subtext smalltext">
          <span>