rest-assured/src/main/java/io/restassured/builder/RequestSpecBuilder.java
public RequestSpecBuilder addHeader(String headerName, String headerValue) {
        spec.header(headerName, headerValue);
        return this;
    }
public RequestSpecBuilder addHeader(String headerName, String headerValue) {
        spec.header(headerName, headerValue);
        return this;
    }
Add a header to be sent with the request e.g:

@param headerName  The header name
@param headerValue The header value
@return The request specification builder