From CLI I get
Enter MFA code for arnawsiam:XXXXXmfa/XXXXX:
{
"UserId": "XXXXXXXXXXXXXX:botocore-session-1553726670",
"Account": "XXXXXXXXXXXXXX",
"Arn": "arnawssts:XXXXXXXXXXXXXXassumed-role/XXXXXXX-sandbox-developer/botocore-session-XXXXXXXXXXXXXX"
}