REST API with Mutual TLS

The sample project is created to showcase how we can build a REST API which enforces Mutual TLS authentication. Mutual TLS authentication requires two-way authentication between the client and the server. In addition to server authentication (where the client verifies the server's identity), mutual TLS requires client authentication (where the server verifies the client's identity). With mutual TLS, clients must present X.509 certificates to verify their identity to access your API. In microservices architectures, use of mutual TLS can secure service to service communication, preventing unauthorized access and data breaches.

Software Used

• Java 17
• Tomcat 10
• OpenSSL

Generate Key Pairs (Private Key, Public Key, Certificate Signing Request & Certificate)

OpenSSL commands handful to generate Key Pair, Certificate Signing Request and Certificate

To view a Private Key openssl rsa -in rootCA.key -text To view a certificate openssl x509 -noout -text -in rootCA.pem

Root KeyPair for Certificate Authority (CA)

• Generate Private Key
  • with passphrase

    openssl genrsa -des3 -out rootCA.key 4096
    

  • without passphrase

    openssl genrsa -out rootCA.key 4096
    

• Generate Certificate

  openssl req -x509 -new -nodes -key rootCA.key -sha512 -days 1825 -out rootCA.crt -subj "/C=US/ST=CA/L=Los Angeles/O=Saviynt Inc/OU=Certificate Authority/CN=saviynt.com/[email protected]" -addext "subjectAltName = DNS:saviynt.com"
  

• Generate Private Key & Certificate using a Single line command

  openssl req -x509 -newkey rsa:4096 -sha512 -nodes -keyout rootCA.key -out rootCA.crt -days 1825 -subj "/C=US/ST=CA/L=Los Angeles/O=Saviynt Inc/OU=Certificate Authority/CN=saviynt.com/[email protected]" -addext "subjectAltName = DNS:saviynt.com"
  

Server's Key & Certificate

• Generate Private Key
  • with passphrase

    openssl genrsa -des3 -out server.key 4096
    

  • without passphrase

    openssl genrsa -out server.key 4096
    

• Generate Certificate Signing Request file

  openssl req -new -sha512 -key server.key -out server.csr \
  -subj "/C=US/ST=CA/L=Los Angeles/O=Saviynt Inc/OU=Saviynt Server/CN=server.saviynt.com/[email protected]" \
  -addext "subjectAltName = DNS:server.saviynt.com"
  

• Generate Certificate

  openssl x509 -req -in server.csr -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out server.crt -days 365 -sha512
  

• Create PKCS12 Key Store for the Server component with Key & Certificate. The server is going to use this KeyStore. Additionally assigning a alias name to refer easily in case Key Store contains multiple KeyPairs.

  openssl pkcs12 -export -in server.crt -inkey server.key -out keystore.p12 -name server-primary-alias
  

Client's Key & Certificate

• Generate Private Key
  • with passphrase

    openssl genrsa -des3 -out client.key 4096
    

  • without passphrase

    openssl genrsa -out client.key 4096
    

• Generate Certificate Signing Request file

  openssl req -new -sha512 -key client.key -out client.csr \
  -subj "/C=US/ST=CA/L=Los Angeles/O=Saviynt Inc/OU=Saviynt Client/CN=client.saviynt.com/[email protected]" \
  -addext "subjectAltName = DNS:client.saviynt.com"
  

• Generate Certificate

  openssl x509 -req -in client.csr -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out client.crt -days 365 -sha512
  

• Create PKCS12 Key Store for the Client component with Key & Certificate. The clinet is going to use this KeyStore. Additionally assigning a alias name to refer easily in case Key Store contains multiple KeyPairs.

  openssl pkcs12 -export -in server.crt -inkey server.key -out keystore.p12 -name server-primary-alias
  

Generate TrustStore

In this example, same CA (Certificate Authority) has been used for signing the Server and Client certificates. Therefore, a Global trust store is distributed to both server and client. You can use different CA for Server and Client as well. In that case you have to distribute Trust Store accordingly.

• Generate TrustStore of PKCS12 type and pass it to server & client.

keytool -import -trustcacerts -alias rootCA -file rootCA.crt -keystore truststore.p12 -storetype PKCS12 -storepass changeit

N.B. - The TrustStore of PKCS12 type can be created using

openssl pkcs12 -export -nokeys -in rootCA.crt -out truststore.p12 -passout pass:changeit

But this can't be read using keytool -list -storetype PKCS12 -keystore truststore.p12 Output looks like below from the above command

Enter keystore password:  
Keystore type: PKCS12
Keystore provider: SUN

Your keystore contains 0 entries

Even java code is facing error like following at server startup.

Caused by: java.security.InvalidAlgorithmParameterException: the trustAnchors parameter must be non-empty
      at java.base/java.security.cert.PKIXParameters.setTrustAnchors(PKIXParameters.java:200) ~[na:na]
      at java.base/java.security.cert.PKIXParameters.<init>(PKIXParameters.java:157) ~[na:na]
      at java.base/java.security.cert.PKIXBuilderParameters.<init>(PKIXBuilderParameters.java:130) ~[na:na]
      at org.apache.tomcat.util.net.SSLUtilBase.getParameters(SSLUtilBase.java:501) ~[tomcat-embed-core-10.1.11.jar:10.1.11]
      at org.apache.tomcat.util.net.SSLUtilBase.getTrustManagers(SSLUtilBase.java:432) ~[tomcat-embed-core-10.1.11.jar:10.1.11]
      at org.apache.tomcat.util.net.SSLUtilBase.createSSLContext(SSLUtilBase.java:246) ~[tomcat-embed-core-10.1.11.jar:10.1.11]
      at org.apache.tomcat.util.net.AbstractJsseEndpoint.createSSLContext(AbstractJsseEndpoint.java:104) ~[tomcat-embed-core-10.1.11.jar:10.1.11]
      ... 25 common frames omitted

Build WAR and Deploy in Tomcat

Build

This command will compile your source code, package it into a WAR file, and place it in the build/libs directory of your project.

./gradlew clean
./gradlew build

Deploy in Tomcat

In this project Tomcat 10 has been used from Tomcat 10. Extract the archive. Copy the WAR file under $CATALINA_HOME/webapps/ Copy the keystore and truststore under $CATALINA_HOME/conf/ Edit $CATALINA_HOME/conf/server.xml to add a Connector element as follows to enable TLS and Client Authentication (i.e. M-TLS).

<Connector 
        port="8443"
        protocol="org.apache.coyote.http11.Http11NioProtocol"
        maxThreads="150"
        SSLEnabled="true"
        scheme="https"
        secure="true"
        clientAuth="true"
        sslProtocol="TLS"
        maxParameterCount="1000">
        <!-- address="0.0.0.0" -->
        <SSLHostConfig
          certificateVerification="required"
          truststoreFile="<path_to_truststore.p12_file>"
          truststoreType="PKCS12"
          truststorePassword="changeit">
            <Certificate 
                certificateKeystoreFile="<path_to_keystore.p12_file>" 
                certificateKeystoreType="PKCS12" 
                certificateKeystorePassword="changeit" 
                type="RSA" />
                <!-- certificateKeyAlias="server-primary-alias"  -->
        </SSLHostConfig>
    </Connector>

Start the server using $CATALINA_HOME/bin/startup.sh.

You can even test the MTLS REST API using curl command like following.

curl -vvv \
--cert store/client.crt \
--key store/client.key \
--cacert store/rootCA.crt \
"https://server.saviynt.com:8443/mtls-rest-server/hello"