Frontend headers generation source

[alexei-moneyr]

After couple hours of gooling and code examination (frontend) it's still unknown how headers are generated.

"Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3", "accept-encoding": "gzip, deflate, br", "Accept-Language": "en-US,en;q=0.9,pt-BR;q=0.8,pt;q=0.7,es-CO;q=0.6,es;q=0.5,zh-CN;q=0.4,zh;q=0.3", "cache-control": "max-age=0", "CloudFront-Forwarded-Proto": "https", "CloudFront-Is-Desktop-Viewer": "true", "CloudFront-Is-Mobile-Viewer": "false", "CloudFront-Is-SmartTV-Viewer": "false", "CloudFront-Is-Tablet-Viewer": "false", "CloudFront-Viewer-Country": "US", "Host": "asdasd.execute-api.us-east-1.amazonaws.com", "sec-fetch-mode": "navigate", "sec-fetch-site": "none", "sec-fetch-user": "?1", "upgrade-insecure-requests": "1", "User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.70 Safari/537.36", "Via": "2.0 af59cbeda88e3a41b2689a63q4f61c64d.cloudfront.net (CloudFront)", "X-Amz-Cf-Id": "NzOz5TfgbqItgmy_C2Zj4TjAnkqMteY-aNMmshY4W9TZ1U-rJr5LHWw==", "X-Amzn-Trace-Id": "Root=1-5dc86974-035aeec025a456001d3ac4b6cb", "X-Forwarded-For": "72.21.196.66, 54.239.145.80", "X-Forwarded-Port": "443", "X-Forwarded-Proto": "https"

There also no documentation for this. any chance getting the answer or direction to dig?
Thanks