import json


def fetch_credentials(service_name, creds_file="service-credentials.json"):
    """Fetch credentials for cloud services from file.
    
    Params
    ======
    - service_name: a Watson service name, e.g. "discovery" or "conversation"
    - creds_file: file containing credentials in JSON format
    
    Returns
    =======
    creds: dictionary containing credentials for specified service
    """
    
    with open(creds_file, "r") as f:
        creds = json.load(f)
        return creds[service_name]