Add user to project role

def myself = Users.getLoggedInUser()

def projectKey = 'TP'
def roleId = '10002'

def result = post("rest/api/3/project/${projectKey}/role/${roleId}")
    .header('Content-Type', 'application/json')
    .body([
        "user": [myself.accountId]
    ])
    .asObject(Map)

result.body