Invalid self signed SSL cert - "Subject Alternative Name Missing"

To fix this, you need to supply an extra parameter to openssl when you're creating the cert, basically

-sha256 -extfile v3.ext

where v3.ext is a file like so, with %%DOMAIN%% replaced with the same name you use as your Common Name. More info here and over here. Note that typically you'd set the Common Name and %%DOMAIN%% to the domain you're trying to generate a cert for. So if it was www.mysupersite.com, then you'd use that for both.

v3.ext

authorityKeyIdentifier=keyid,issuer
basicConstraints=CA:FALSE
keyUsage = digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment
subjectAltName = @alt_names

[alt_names]
DNS.1 = %%DOMAIN%%

Note: Scripts that address this issue, and create fully trusted ssl certs for use in Chrome, Safari and from Java clients can be found here

Another note: If all you're trying to do is stop chrome from throwing errors when viewing a self signed certificate, you can can tell Chrome to ignore all SSL errors for ALL sites by starting it with a special command line option, as detailed here on SuperUser

Following solution worked for me on chrome 65 (ref) -

Create an OpenSSL config file (example: req.cnf)

[req]
distinguished_name = req_distinguished_name
x509_extensions = v3_req
prompt = no
[req_distinguished_name]
C = US
ST = VA
L = SomeCity
O = MyCompany
OU = MyDivision
CN = www.company.com
[v3_req]
keyUsage = critical, digitalSignature, keyAgreement
extendedKeyUsage = serverAuth
subjectAltName = @alt_names
[alt_names]
DNS.1 = www.company.com
DNS.2 = company.com
DNS.3 = company.net

Create the certificate referencing this config file

openssl req -x509 -nodes -days 730 -newkey rsa:2048 \
 -keyout cert.key -out cert.pem -config req.cnf -sha256