How To Create an SSL Certificate on Apache for CentOS 7

原文: https://www.digitalocean.com/community/tutorials/how-to-create-an-ssl-certificate-on-apache-for-centos-7
Introduction

TLS, or "transport layer security", and its predecessor SSL, which stands for "secure sockets layer", are web protocols used to wrap normal traffic in a protected, encrypted wrapper. Using this technology, servers can send traffic safely between the server and the client without the concern that the messages will be intercepted and read by an outside party. The certificate system also assists users in verifying the identity of the sites that they are connecting with.

In this guide, we will show you how to set up a self-signed SSL certificate for use with an Apache web server on a CentOS 7 VPS. A self-signed certificate will not validate the identity of your server, since it is not signed by a trusted certificate authorities, but it will allow you to encrypt communications between your server and your visitors.

Prerequisites
Before you begin with this guide, there are a few steps that need to be completed first.

You will need access to a CentOS 7 server with a non-root user that has sudo privileges. If you haven't configured this yet, you can run through the CentOS 7 initial server setup guide to create this account.

You will also need to have Apache installed in order to configure virtual hosts for it. If you haven't already done so, you can use yum to install Apache through CentOS's default software repositories:

sudo yum install httpd
Next, enable Apache as a CentOS service so that it will automatically start after a reboot:

sudo systemctl enable httpd.service
After these steps are complete, you can log in as your non-root user account through SSH and continue with the tutorial.

Step One — Install Mod SSL
In order to set up the self-signed certificate, we first have to be sure that mod_ssl, an Apache module that provides support for SSL encryption, is installed on our VPS. We can install mod_ssl with the yum command:

sudo yum install mod_ssl
The module will automatically be enabled during installation, and Apache will be able to start using an SSL certificate after it is restarted. You don't need to take any additional steps for mod_ssl to be ready for use.

Step Two — Create a New Certificate
Now that Apache is ready to use encryption, we can move on to generating a new SSL certificate. The certificate will store some basic information about your site, and will be accompanied by a key file that allows the server to securely handle encrypted data.

First, we need to create a new directory where we will store the server key and certificate:

sudo mkdir /etc/httpd/ssl
Now that we have a location to place our files, we can create the SSL key and certificate files with openssl:

sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/httpd/ssl/apache.key -out /etc/httpd/ssl/apache.crt
After you enter the request, you will be taken to a prompt where you can enter information about your website. Before we go over that, let's take a look at what is happening in the command we are issuing:

openssl: This is the basic command line tool for creating and managing OpenSSL certificates, keys, and other files.
req -x509: This specifies that we want to use X.509 certificate signing request (CSR) management. The "X.509" is a public key infrastructure standard that SSL and TLS adhere to for key and certificate management.
-nodes: This tells OpenSSL to skip the option to secure our certificate with a passphrase. We need Apache to be able to read the file, without user intervention, when the server starts up. A passphrase would prevent this from happening, since we would have to enter it after every restart.
-days 365: This option sets the length of time that the certificate will be considered valid. We set it for one year here.
-newkey rsa:2048: This specifies that we want to generate a new certificate and a new key at the same time. We did not create the key that is required to sign the certificate in a previous step, so we need to create it along with the certificate. The rsa:2048 portion tells it to make an RSA key that is 2048 bits long.
-keyout: This line tells OpenSSL where to place the generated private key file that we are creating.
-out: This tells OpenSSL where to place the certificate that we are creating.
Fill out the prompts appropriately. The most important line is the one that requests the Common Name. You need to enter the domain name that you want to be associated with your server. You can enter the public IP address instead if you do not have a domain name.

The full list of prompts will look something like this:

Country Name (2 letter code) [XX]:US
State or Province Name (full name) []:Example
Locality Name (eg, city) [Default City]:Example
Organization Name (eg, company) [Default Company Ltd]:Example Inc
Organizational Unit Name (eg, section) []:Example Dept
Common Name (eg, your name or your server's hostname) []:example.com
Email Address []:webmaster@example.com
Step Three — Set Up the Certificate
We now have all of the required components of the finished interface. The next thing to do is to set up the virtual hosts to display the new certificate.

Open Apache's SSL configuration file in your text editor with root privileges:

sudo nano /etc/httpd/conf.d/ssl.conf
Find the section that begins with <VirtualHost _default_:443>. We need to make a few changes here to ensure that our SSL certificate is correctly applied to our site.

First, uncomment the DocumentRoot line and edit the address in quotes to the location of your site's document root. By default, this will be in /var/www/html, and you don't need to change this line if you have not changed the document root for your site. However, if you followed a guide like our Apache virtual hosts setup guide, your site's document root may be different.

DocumentRoot "/var/www/example.com/public_html"
Next, uncomment the ServerName line and replace www.example.com with your domain name or server IP address (whichever one you put as the common name in your certificate):

ServerName www.example.com:443
Find the SSLCertificateFile and SSLCertificateKeyFile lines and change them to the directory we made at /etc/httpd/ssl:

SSLCertificateFile /etc/httpd/ssl/apache.crt
SSLCertificateKeyFile /etc/httpd/ssl/apache.key
When you are finished making these changes, you can save and close the file.

Step Four — Activate the Certificate
By now, you have created an SSL certificate and configured your web server to apply it to your site. To apply all of these changes and start using your SSL encryption, you can restart the Apache server to reload its configurations and modules:

sudo apachectl restart
In your web browser, try visiting your domain name or IP with https:// to see your new certificate in action.

https://example.com/
Your web browser will likely warn you that the site's security certificate is not trusted. Since your certificate isn't signed by a certificate authority that the browser trusts, the browser is unable to verify the identity of the server that you are trying to connect to. We created a self-signed certificate instead of a trusted CA-signed certificate, so this makes perfect sense.

Once you add an exception to the browser's identity verification, you will be allowed to proceed to your newly secured site.

Conclusion
You have configured your Apache server to handle both HTTP and HTTPS requests. This will help you communicate with clients securely and avoid outside parties from being able to read your traffic.

If you are planning on using SSL for a public website, you should probably purchase an SSL certificate from a trusted certificate authority to prevent the scary warnings from being shown to each of your visitors.