Image Blog Mutual Authentication Using Apache and a Web Client
November 25, 2015

Mutual Authentication Using Apache and a Web Client

Web Infrastructure

Mutual authentication using Apache and a web client can be tricky. In this blog, we walk through the Apache client certificate authentication process and how to do it.

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What Is Client Certificate Authentication?

Client certificate authentication refers to a certificate used to authenticate clients in SSL. 

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How to Do Apache Client Certificate Authentication

All that is taking place here beyond standard SSL is that the server will also authenticate the client that is requesting access.

1. Requirements for Authentication

First, some assumptions must be made to get this up and running. You will need to have the following:

An Apache instance that has mod_ssl enabled.

Verification: run the following


 apachectl –M | grep ssl

You should see something like this:

ssl_module (shared)

If you don’t have this then you will need to get this enabled in order to continue.

Proper access.



• Apache
• OpenSSL
• The certs that you will create and install


2. Generate the Certificate

Let's begin with the documented steps below:

Generate the certificate for the self signed CA.

openssl req -newkey rsa:2048 -nodes -keyform PEM -keyout selfsigned-ca.key -x509 -days 3650    -outform PEM -out selfsigned-ca.crt


New items:
• selfsigned-ca.key
• selfsigned-ca.crt
• The CA has now been created

Create the SSL server's private key.

openssl genrsa -out selfsigned.key 2048


New items:
• selfsigned.key

Create the Apache server CSR.

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


New items:
• selfsigned.csr

Sign the Apache server CSR.

openssl x509 -req -in selfsigned.csr -CA selfsigned-ca.crt -CAkey selfsigned-ca.key -set_serial 100 -days 365 -outform PEM -out selfsigned.crt


New items:
• selfsigned.crt
• The cert is good for 10 years.


3. Configure Apache

Now, looking at this from the Apache SSL point of view, what we have below is sufficient for one-way or standard SSL communications.

Apache configuration

Place your certificate and key generated from above into the location below.


If you need to place it somewhere else, be sure to modify the path for the two SSL directives below.

Either way, change those two directives in your httpd configuration in Path/to/apache/conf/extra/httpd-ssl.conf or in your vhost configuration if that is where you are enabling use of SSL.

SSLCertificateFile "/etc/pki/tls/rselfsigned.crt”
SSLCertificateKeyFile "/etc/pki/tls/selfsigned.key”

This is sufficient for one-way SSL communications.

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4. Make Sure SSL Works

Let's check Apache and make sure SSL is working properly:

Ensure that the SSL-enabled Apache instance works.

Verification: run the following


Openssl s_client –connect

You should see:


And a bunch of other text and a BEGIN CERTIFICATE block. If you do, all is well.

If this does not work, then you must get SSL in working order before you can continue.

At this point SSL is functioning properly on the Apache web server.

5. Begin Mutual Authentication

In your SSL configuration file (the local selected above) add the following:

• SSLVerifyClient
• SSLVerifyDepth 10
• SSLCACertificateFile /path/to/cert/selfsigned-ca.crt

Once again, follow the documented steps below:

Generate the client's private key.

openssl genrsa -out selfsigned-cli.key 2048


New items:
• selfsigned-cli.key

Create the client CSR.

openssl req -new -key selfsigned-cli.key -out selfsigned-cli.csr


New items:
• selfsigned-cli.csr

Sign the client CSR.

openssl x509 -req -in selfsigned-cli.csr -CA selfsigned-ca.crt -CAkey selfsigned-ca.key -set_serial 101 -days 365 -outform PEM -out selfsigned-cli.crt


New items:
• selfsigned-cli.crt

Bundle the client's certificate and client's key into a p12 pack.

openssl pkcs12 -export -inkey selfsigned-cli.key -in selfsigned-cli.crt -out selfsigned-cli.p12


New items:
• selfsigned-cli.p12


6. Test the Apache Certificate Authentication

Restart Apache with: apachectl restart.

Attempt to access it via https. You will be prevented from doing so without the client side certificate you just created because Apache is looking for it in the exchange.

Add the new certificate bundle (selfsigned-cli.p12) to your keychain on your workstation. Now, in your browser access the https URL once again. You will be challenged with something like this:


Apache certificate

Since the certificate is on my keychain, I can simply select it from the list. (Above are three copies of the same not sure how that occurred, just ignore the others.)

After picking the certificate, VIOLA! I now have access via mutual authentication.

That is how to setup mutual authentication using Apache and a web client.

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Go Beyond Apache Client Certificate Authentication

Authentication can be tricky, whether you're using Apache client certificates or microservices. 

Authentication is especially important for security in microservices. 


Get More Guidance

In our white paper, Wildfly for Microservices Authentication, learn: 

  • About your options for microservices authentication.
  • When it can be advantageous to use Mutual TLS for client certificate authentication instead of TLS or JWT.
  • A step-by-step tutorial for implementing Mutual TLS authentication.
  • How to manage certificates with Wildfly Elytron Client SSL Contexts.

Get the White Paper

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