Consuming webservice in dot net API

Question

I have created An API,and under this API i want to consume the web service. From the API I am passing int a from header and int b from route. But the webservice is expecting the credentials(username and password) also.And in API request parameter we are not passing it from api request and we can't set the username and password hard-coded in code. Can anyone suggest me how can I proceed for this? Thanks in advance.