Getting Chrome to accept self-signed localhost certificate

This worked for me:

1. Using Chrome, hit a page on your server via HTTPS and continue past the red warning page (assuming you haven't done this already).
2. Open up Chrome Settings > Show advanced settings > HTTPS/SSL > Manage Certificates.
3. Click the Authorities tab and scroll down to find your certificate under the Organization Name that you gave to the certificate.
4. Select it, click Edit (NOTE: in recent versions of Chrome, the button is now "Advanced" instead of "Edit"), check all the boxes and click OK. You may have to restart Chrome.

You should get the nice green lock on your pages now.

EDIT: I tried this again on a new machine and the certificate did not appear on the Manage Certificates window just by continuing from the red untrusted certificate page. I had to do the following:

1. On the page with the untrusted certificate (https:// is crossed out in red), click the lock > Certificate Information. NOTE: on newer versions of chrome, you have to open Developer Tools > Security, and select View certificate.
2. Click the Details tab > Export. Choose PKCS #7, single certificate as the file format.
3. Then follow my original instructions to get to the Manage Certificates page. Click the Authorities tab > Import and choose the file to which you exported the certificate, and make sure to choose PKCS #7, single certificate as the file type.
4. If prompted certification store, choose Trusted Root Certificate Authorities
5. Check all boxes and click OK. Restart Chrome.

UPDATE FOR CHROME 58+ (RELEASED 2017-04-19)

As of Chrome 58, the ability to identify the host using only commonName was removed. Certificates must now use subjectAltName to identify their host(s). See further discussion here and bug tracker here. In the past, subjectAltName was used only for multi-host certs so some internal CA tools don't include them.

If your self-signed certs worked fine in the past but suddenly started generating errors in Chrome 58, this is why.

So whatever method you are using to generate your self-signed cert (or cert signed by a self-signed CA), ensure that the server's cert contains a subjectAltName with the proper DNS and/or IP entry/entries, even if it's just for a single host.

For openssl, this means your OpenSSL config (/etc/ssl/openssl.cnf on Ubuntu) should have something similar to the following for a single host:

[v3_ca]   # and/or [v3_req], if you are generating a CSR
subjectAltName = DNS:example.com

or for multiple hosts:

[v3_ca]   # and/or [v3_req], if you are generating a CSR
subjectAltName = DNS:example.com, DNS:host1.example.com, DNS:*.host2.example.com, IP:10.1.2.3

In Chrome's cert viewer (which has moved to "Security" tab under F12) you should see it listed under Extensions as Certificate Subject Alternative Name:

Click anywhere on the page and type a BYPASS_SEQUENCE

"thisisunsafe" is a BYPASS_SEQUENCE for Chrome version 65

"badidea" Chrome version 62 - 64.

"danger" used to work in earlier versions of Chrome

You don't need to look for input field, just type it. It feels strange but it is working.

I tried it on Mac High Sierra.

To double check if they changed it again go to Latest chromium Source Code

To look for BYPASS_SEQUENCE, at the moment it looks like that:

var BYPASS_SEQUENCE = window.atob('dGhpc2lzdW5zYWZl');

Now they have it camouflaged, but to see the real BYPASS_SEQUENCE you can run following line in a browser console.

console.log(window.atob('dGhpc2lzdW5zYWZl'));

On the Mac, you can use the Keychain Access utility to add the self-signed certificate to the System keychain, and Chrome will then accept it. I found the step-by-step instructions here:

Google Chrome, Mac OS X and Self-Signed SSL Certificates

Basically:

1. double-click the lock icon with an X and drag-and-drop the certificate icon to the desktop,
2. open this file (ending with a .cer extension); this opens the keychain application which allows you to approve the certificate.

On the Mac, you can create a certificate that's fully trusted by Chrome and Safari at the system level by doing the following:

    # create a root authority cert
    ./create_root_cert_and_key.sh
    
    # create a wildcard cert for mysite.com
    ./create_certificate_for_domain.sh mysite.com
    
    # or create a cert for www.mysite.com, no wildcards
    ./create_certificate_for_domain.sh www.mysite.com www.mysite.com

The above uses the following scripts, and a supporting file v3.ext, to avoid subject alternative name missing errors

If you want to create a new self signed cert that's fully trusted using your own root authority, you can do it using these scripts.

create_root_cert_and_key.sh

    #!/usr/bin/env bash
    openssl genrsa -out rootCA.key 2048
    openssl req -x509 -new -nodes -key rootCA.key -sha256 -days 1024 -out rootCA.pem

create_certificate_for_domain.sh

    #!/usr/bin/env bash
    
    if [ -z "$1" ]
    then
      echo "Please supply a subdomain to create a certificate for";
      echo "e.g. www.mysite.com"
      exit;
    fi
    
    if [ ! -f rootCA.pem ]; then
      echo 'Please run "create_root_cert_and_key.sh" first, and try again!'
      exit;
    fi
    if [ ! -f v3.ext ]; then
      echo 'Please download the "v3.ext" file and try again!'
      exit;
    fi
    
    # Create a new private key if one doesnt exist, or use the xeisting one if it does
    if [ -f device.key ]; then
      KEY_OPT="-key"
    else
      KEY_OPT="-keyout"
    fi
    
    DOMAIN=$1
    COMMON_NAME=${2:-*.$1}
    SUBJECT="/C=CA/ST=None/L=NB/O=None/CN=$COMMON_NAME"
    NUM_OF_DAYS=825
    openssl req -new -newkey rsa:2048 -sha256 -nodes $KEY_OPT device.key -subj "$SUBJECT" -out device.csr
    cat v3.ext | sed s/%%DOMAIN%%/"$COMMON_NAME"/g > /tmp/__v3.ext
    openssl x509 -req -in device.csr -CA rootCA.pem -CAkey rootCA.key -CAcreateserial -out device.crt -days $NUM_OF_DAYS -sha256 -extfile /tmp/__v3.ext 
    
    # move output files to final filenames
    mv device.csr "$DOMAIN.csr"
    cp device.crt "$DOMAIN.crt"
    
    # remove temp file
    rm -f device.crt;
    
    echo 
    echo "###########################################################################"
    echo Done! 
    echo "###########################################################################"
    echo "To use these files on your server, simply copy both $DOMAIN.csr and"
    echo "device.key to your webserver, and use like so (if Apache, for example)"
    echo 
    echo "    SSLCertificateFile    /path_to_your_files/$DOMAIN.crt"
    echo "    SSLCertificateKeyFile /path_to_your_files/device.key"

v3.ext

    authorityKeyIdentifier=keyid,issuer
    basicConstraints=CA:FALSE
    keyUsage = digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment
    subjectAltName = @alt_names
    
    [alt_names]
    DNS.1 = %%DOMAIN%%

One more step - How to make the self signed certs fully trusted in Chrome/Safari

To allow the self signed certificates to be FULLY trusted in Chrome and Safari, you need to import a new certificate authority into your Mac. To do so follow these instructions, or the more detailed instructions on this general process on the mitmproxy website:

You can do this one of 2 ways, at the command line, using this command which will prompt you for your password:

$ sudo security add-trusted-cert -d -r trustRoot -k /Library/Keychains/System.keychain rootCA.pem

or by using the Keychain Access app:

1. Open Keychain Access
2. Choose "System" in the "Keychains" list
3. Choose "Certificates" in the "Category" list
4. Choose "File | Import Items..."
5. Browse to the file created above, "rootCA.pem", select it, and click "Open"
6. Select your newly imported certificate in the "Certificates" list.
7. Click the "i" button, or right click on your certificate, and choose "Get Info"
8. Expand the "Trust" option
9. Change "When using this certificate" to "Always Trust"
10. Close the dialog, and you'll be prompted for your password.
11. Close and reopen any tabs that are using your target domain, and it'll be loaded securely!

and as a bonus, if you need java clients to trust the certificates, you can do so by importing your certs into the java keystore. Note this will remove the cert from the keystore if it already exists, as it needs to to update it in case things change. It of course only does this for the certs being imported.

import_certs_in_current_folder_into_java_keystore.sh

KEYSTORE="$(/usr/libexec/java_home)/jre/lib/security/cacerts";

function running_as_root()
{
  if [ "$EUID" -ne 0 ]
    then echo "NO"
    exit
  fi

  echo "YES"
}

function import_certs_to_java_keystore
{
  for crt in *.crt; do 
    echo prepping $crt 
    keytool -delete -storepass changeit -alias alias__${crt} -keystore $KEYSTORE;
    keytool -import -file $crt -storepass changeit -noprompt --alias alias__${crt} -keystore $KEYSTORE
    echo 
  done
}

if [ "$(running_as_root)" == "YES" ]
then
  import_certs_to_java_keystore
else
  echo "This script needs to be run as root!"
fi