rest-assured/src/main/java/io/restassured/specification/ProxySpecification.java
public ProxySpecification withAuth(String username, String password) {
        AssertParameter.notNull(username, "username");
        AssertParameter.notNull(password, "password");
        return new ProxySpecification(host, port, scheme, username, password);
    }
public ProxySpecification withAuth(String username, String password) {
        AssertParameter.notNull(username, "username");
        AssertParameter.notNull(password, "password");
        return new ProxySpecification(host, port, scheme, username, password);
    }
Specify (preemptive) basic authentication for the proxy

@param username The username
@param password The username
@return A new ProxySpecification instance