"Accept" header appears to be overridden using setExtraHTTPHeaders, but isn't

Steps to reproduce

Tell us about your environment:

• Puppeteer version: 1.14.0
• Platform / OS version: Laravel Homestead/Ubuntu 4.4.0-66-generic #87
• URLs (if applicable):
• Node.js version: v11.13.0

What steps will reproduce the problem?

await eloquaPage.setExtraHTTPHeaders(
        {
            'Accept': 'application/json' // also tried 'accept', accept, Accept, "accept", "Accept"
        });
// let thisResponse = await page.goto(<url>);
// console.log(thisResponse.request().headers()); <= shows the overridden header, as expected

What is the expected result? Accept => javascript/json

What happens instead? (as logged in a php built-in test server) [accept] => text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,/;q=0.8,application/signed-exchange;v=b3

I am able to overwrite other headers, and add new headers. If I am doing something wrong, please let me know. I see https://github.com/GoogleChrome/puppeteer/issues/3638 but it was closed without a resolution that I can see.

[mkirkland4874]

I get the same error. This is how I got around it:

await page.setRequestInterception(true);
page.on('request', request => {
  const headers = Object.assign({}, request.headers(), {
    accept: 'application/json',
  });
  request.continue({headers}); // Works
});

const headers = { 'accept': 'application/json' };
await page.setExtraHTTPHeaders(headers); // Does not work

[panthony]

Not sure if related or not but is that the reason why accept, accept-language and accept-encoding do not appears when you call request.headers()?

I’d like to know which headers where sent but the return of this methods seems incomplete…