SSL termination is the recommended method of encrypting communication between users’ browsers and Guacamole, and involves configuring a reverse proxy like Nginx or Apache to handle strictly the SSL/TLS portion of the conversation with the Tomcat instance hosting Guacamole, handling encrypted HTTP externally while passing unencrypted HTTP to Tomcat internally.

Proxying Guacamole through NGINX

If Nginx has been configured for SSL/TLS, there should be a server section within this configuration that defines the certificate and private key used by Nginx, and which requires Nginx to listen on the standard HTTPS port (443). To proxy Guacamole through Nginx such that Guacamole communication is encrypted, a new location section will need to be added within this server section:

location / {
    proxy_pass http://HOSTNAME:8080;
    proxy_buffering off;
    proxy_http_version 1.1;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection $http_connection;
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-Host $host;
    proxy_set_header X-Forwarded-Server $host;
    proxy_set_header X-Forwarded-Proto $scheme;
    access_log off;
    client_max_body_size 200m;
}

where “HOSTNAME” is the hostname or IP address of the internal Guacamole server. This can also be replaced with "http://127.0.0.1:8080" in most cases.

While a typical proxy configuration for Nginx may only specify the proxy_pass and proxy_http_version directives, Guacamole requires additional configuration due to the nature of the application:

• proxy_buffering off disables buffering of packets sent to/from Guacamole. By default, Nginx will buffer communication between itself and the browser, effectively disrupting the stream of events and updates required for remote desktop. Without disabling buffering, the Guacamole connection will at best be slow, and at worst not function at all.

• The X-Forwarded-For header must be explicitly set to ensure that the IP addresses logged by Guacamole are correct. Without explicitly adding this header (and configuring Tomcat to trust this header), all connections will appear to come from the NGINX server.

• The Upgrade and Connection headers are required parts of the WebSocket protocol. If omitted, WebSocket will not function correctly, and Guacamole will fall back to HTTP streaming, which is less efficient.

Applying the updated NGINX configuration

After the above changes have been made, NGINX must be reloaded to force rereading of its configuration files:

$ sudo systemctl reload nginx

If you are using SELinux (the default on both CentOS and RHEL), you must also configure SELinux to allow HTTPD implementations like Nginx to establish network connections:

$ sudo setsebool -P httpd_can_network_connect 1

If Guacamole is not accessible through NGINX after the service has been reloaded, check the NGINX logs and/or journalctl to verify that the syntax of your configuration changes is correct. Such errors will result in NGINX refusing to reload its configuration, or refusing to start up entirely. If you do not see any errors from NGINX, verify that you have configured SELinux to allow NGINX to connect to the network and check the SELinux audit logs (/var/log/audit/audit.log) for AVC denials.

Configuring Tomcat to trust "X-Forwarded-For" from NGINX (manual deployment only)

For the client address sent by NGINX via "X-Forwarded-For" to be correctly trusted as the true client address, you will need to add a "RemoteIpValve" entry within /etc/tomcat/server.xml. If this is not specified, the client address will be logged as the address of the internal proxy, which is not usually desirable.

$ sudo cp /opt/keeper/share/guacamole/server.xml /etc/tomcat/

<Valve className="org.apache.catalina.valves.RemoteIpValve"/>

        ...

        <Valve className="org.apache.catalina.valves.RemoteIpValve"/>

      </Host>
    </Engine>
  </Service>
</Server>

<Valve className="org.apache.catalina.valves.RemoteIpValve"
       internalProxies="127\.\d{1,3}\.\d{1,3}\.\d{1,3}|0:0:0:0:0:0:0:1|::1"/>

Applying the updated Tomcat configuration

Once an appropriate RemoteIpValve has been specified, Tomcat must be restarted to force rereading of server.xml:

$ sudo systemctl restart tomcat

Nginx is not directly available within the CentOS or RHEL repositories, but is available within the EPEL repository. The EPEL repository must be enabled first before Nginx can be installed:

$ sudo yum install epel-release

Once EPEL has been enabled, Nginx can be installed by installing the "nginx" package. Installing this package will install a version of Nginx that is newer than version 1.3 and thus is explicitly supported by Keeper Connection Manager:

$ sudo yum install nginx

As with other standard CentOS / RHEL packages providing a service, the Nginx service will not be started by default after the "nginx" package is installed. It must be started manually, and then configured to automatically start if the system is rebooted:

$ sudo systemctl start nginx
$ sudo systemctl enable nginx

By default, Nginx will listen on port 80 and handle only unencrypted HTTP connections, serving the static contents of /usr/share/nginx/html. The rest of this document will cover reconfiguring Nginx such that it serves only HTTPS (using HTTP only to redirect browsers back to HTTPS), with a placeholder for the minimal additional configuration needed to provide SSL termination. The resulting configuration will be used instead of Nginx' default configuration, and will be split up across two modular files:

Configure Nginx to redirect all HTTP traffic to HTTPS

The main configuration file for Nginx, /etc/nginx/nginx.conf, contains a server block which serves the contents of /usr/share/nginx/html over HTTP:

    server {
        listen       80 default_server;
        listen       [::]:80 default_server;
        server_name  _;
        root         /usr/share/nginx/html;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
        }

        error_page 404 /404.html;
        location = /404.html {
        }

        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
        }
    }

The contents of this server block will conflict with the HTTP redirect that will need to be created, and should be commented-out or removed. Comment out every line with a # at the beginning:

#    server {
#        listen       80 default_server;
#        listen       [::]:80 default_server;
#        server_name  _;
#        root         /usr/share/nginx/html;
#
#        # Load configuration files for the default server block.
#        include /etc/nginx/default.d/*.conf;
#
#        location / {
#        }
#
#        error_page 404 /404.html;
#        location = /404.html {
#        }
#
#        error_page 500 502 503 504 /50x.html;
#        location = /50x.html {
#        }
#    }

With the conflicting server block removed, create a new file, /etc/nginx/conf.d/redirect-http.conf, to contain the new server block and redirect. The server block required is fairly straightforward. Rather than serve static content, it instructs Nginx to issue an HTTP 301 redirect ("Moved Permanently") for all requests, informing the browser that whatever they are requesting can instead be found at the same location using HTTPS:

server {

    listen 80;

    # Redirect all other traffic to HTTPS
    location / {
        return 301 https://$host$request_uri;
    }

}

To apply the new configuration, simply reload Nginx:

$ sudo systemctl reload nginx

Configure Nginx to accept HTTPS connections

To configure Nginx to accept HTTPS connections, you must obtain an SSL certificate for the domain associated with your server. There are two primary ways of doing this:

1. Let's Encrypt: A non-profit certificate authority that provides automated certificate issuance and renewal. Let's Encrypt certificates are free.

2. Obtaining a certificate from a certificate authority: Several commercial certificate authorities exist, many of which are also domain registrars. Unlike Let's Encrypt, obtaining a certificate from a commercial certificate authority will usually cost money.

$ sudo yum install certbot

server {

    listen 80;

    # Let's Encrypt requires access to /.well-known/ for its webroot plugin
    location /.well-known/ {
        root /usr/share/nginx/html;
        break;
    }

    # Redirect all other traffic to HTTPS
    location / {
        return 301 https://$host$request_uri;
    }

}

$ sudo systemctl reload nginx

$ sudo certbot certonly -d remote.example.com --webroot --webroot-path /usr/share/nginx/html

server {

    listen 443 ssl;

    # Location block pointing to Tomcat will go here

    ssl_certificate /etc/letsencrypt/live/remote.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/remote.example.com/privkey.pem;

}

#!/bin/bash

# Attempt to renew certificates daily, reloading Nginx if an updated
# certificate is issued
certbot renew --quiet && systemctl reload nginx

$ sudo chmod +x /etc/cron.daily/certbot

server {

    listen 443 ssl;

    # Location block pointing to Tomcat will go here

    ssl_certificate /etc/pki/tls/certs/remote-example-com-cert.pem;
    ssl_certificate_key /etc/pki/tls/private/remote-example-com-key.pem;

}

Finalizing the configuration (pointing Nginx at Guacamole)

With Nginx now deployed with a proper SSL certificate, the final step in providing SSL termination for Guacamole is to configure Nginx as a reverse proxy for Guacamole. This process involves adding a location block within the Nginx server block for HTTPS, in this case the /etc/nginx/conf.d/guacamole.conf configuration file that was just created. Documentation is provided for the full content and meaning of the required location block, which should be added in the space noted by the "Location block pointing to Tomcat will go here" placeholder comments above.

Client Certificate Overview

To implement device-based access security with Keeper Connection Manager, this can be accomplished using NGINX client certificates. A client certificate is installed into the web browser of your user's approved devices, and the server will only accept communication from a device with the client certificate installed.

The steps to activate this advanced level of protection is described in the steps below.

(1) Create a Certificate Authority (CA) Key

Generate a CA Key with a strong auto-generated passphrase. Make sure to store the passphrase in your Keeper vault.

openssl genrsa -des3 -out ca.key 4096

(2) Create a CA Certificate

A certificate is created with the CA Key. When answering the questions, you can leave the Common Name and Email empty. Save the information that you entered for Country, State, Locality, and Organization, because you may need these later when renewing the certificate.

openssl req -new -x509 -days 365 -key ca.key -out ca.crt

Side Note: to analyze the certificate parameters, you can run the below command.

openssl x509 -in ca.crt -noout -text

(3) Create a Client Key

For the end-user devices, a client key must be generated. You can decide if you would like to generate one key for all devices, or each user can generate their own key and request a certificate. The process is up to you. Generate a client key with a strong auto-generated passphrase. Make sure to store the passphrase in your Keeper vault.

openssl genrsa -des3 -out client.key 4096

(4) Create a CSR

For each Client Key, generate a CSR to create a signed certificate.

openssl req -new -key client.key -out client.csr

(5) Sign the CSR with the CA Key

openssl x509 -req -days 365 -in client.csr \
 -CA ca.crt -CAkey ca.key \
 -set_serial 01 -out client.crt

You'll need to enter the CA passphrase from Step 1 to sign the request.

At this point, you now have a signed Client Certificate (client.crt).

(6) Convert the Client Certificate to PKCS#12

To import the certificate into a web browser, a pfx file in PKCS#12 is typically required. Generate the client.pfx file using the command below. A passphrase will be required. This passphrase will be provided to each of the users who need to install the certificate, so it should be used specifically for this purpose.

openssl pkcs12 -export -clcerts -in client.crt -inkey client.key -out client.pfx

(7) Add to NGINX Config

Add the below line to your Keeper Connection Manager NGINX configuration file to block access without a certificate. Make sure to upload the CA certificate to the folder path designated.

ssl_client_certificate /etc/nginx/client_certs/ca.crt;
ssl_verify_client optional;

In the Location block, add this section to send the user a 403 error if the client cert is not installed:

        if ($ssl_client_verify != SUCCESS) {
                return 403;
        }

Make sure that the ca.crt file is located in a folder that NGINX can access.

After updating the configuration, restart NGINX.

sudo systemctl restart nginx

(8) Test the configuration

Before installing the client certificate on the user's machine, load up the Keeper Connection Manager login screen to ensure that a 403 error is sent:

(9) Install the Client Certificate

For each end-user client device that will need access to Keeper Connection Manager, you will need to install the client certificate into the user's browser or machine. The installation of client certificates varies by platform.

On Windows

Double-click or right-click the client certificate (client.pfx) from Step 6 and enter the client certificate passphrase.

Restart the browser.

The next time Keeper Connection Manager is loaded, you can approve the certificate.

On Mac OS - Chrome

Import the client.pfx file by double-clicking or loading into the Keychain login Certificates section. In the "Trust" section of the certificate, mark as Always Trust.

Restart the browser and load the Keeper Connection Manager login screen to select the certificate.

On Mac OS - Firefox

Open Firefox > Preferences > search for Certificates and select Your Certificates tab. Click "Import" and select the client.pfx certificate file. Complete the import.

After successful import, the Keeper Connection Manager login screen will load.

Troubleshooting

After setting up the client certificate configuration, the following errors are common.

If NGINX fails to start, journalctl -xe might show something like "Permission denied:fopen('/path/to/ca.crt','r'). This might occur if the folder permissions and file permissions are not set properly.

If the folder and file permissions are set properly and you're still receiving this error, the restorecon command will repair the SELinux security context for the file:

restorecon ca.crt