opensslcommand.txt

genrsa -out key.txt 512
rsa -in key.txt -out key.txt
req -sha256 -new -things -key key.txt -out cert.csr -subj '/C=UA/ST=K/L=Kiev/O=yourcompanyname [RO]/OU=OWLOS/CN=OWLOS.local' -addext subjectAltName=DNS:OWLOS.local,IP:192.168.4.1
x509 -req -sha256 -days 365 -in cert.csr -signkey key.txt -out cert.txt

genrsa -out key.txt 512
rsa -in key.txt -out key.txt
req -sha256 -new -things -key key.txt -out cert.csr -subj '/C=UA/ST=K/L=Kiev/O=yourcompanyname [RO]/OU=OWLOS/CN=OWLOS.local' -addext subjectAltName=DNS:OWLOS.local,IP:192.168.4.1
x509 -req -sha256 -days 365 -in cert.csr -signkey key.txt -out cert.txt


^^^
Copy to OpenSSL command prompt, the cert.txt and key.txt files will be created
https://slproweb.com/products/Win32OpenSSL.html
^^^
Install OpenSLL for Windows 
Documentation: https://www.onetransistor.eu/2019/04/https-server-on-esp8266-thingmcu.html
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-subj:
    C - country, short name
    ST - state or province
    L - locality or city
    O - organization
    OU - organizational thing
    CN - common name (domain name)

The subjectAltName parameter must contain the domain name(s) where your server is accessible. It can specify also IP addresses like this: subjectAltName=DNS:esp8266.local,IP=192.168.4.1. When requesting a webpage secured with this certificate, the browser will complain it does not know the CA ("ERR_CERT_AUTHORITY_INVALID" is the message displayed by Google Chrome).