rest-assured/src/main/java/io/restassured/specification/ProxySpecification.java
public static ProxySpecification auth(String username, String password) {
        AssertParameter.notNull(username, "username");
        AssertParameter.notNull(password, "password");
        return new ProxySpecification(DEFAULT_HOST, DEFAULT_PORT, DEFAULT_SCHEME, username, password);
    }
public static ProxySpecification auth(String username, String password) {
        AssertParameter.notNull(username, "username");
        AssertParameter.notNull(password, "password");
        return new ProxySpecification(DEFAULT_HOST, DEFAULT_PORT, DEFAULT_SCHEME, username, password);
    }
Specify preemptive basic authentication for the proxy. Will use hostname {@value #DEFAULT_HOST}, port {@value #DEFAULT_PORT} and scheme {@value #DEFAULT_SCHEME}.

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