Install a free Let's Encrypt SSL certificate for Spring Boot

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1- The objective of the article

Let’s Encrypt is a free SSL certificate provider developed by the Internet Security Research Group (ISRG)Let's Encrypt provides two types of certificates that are SSL for standard domain names, and Wildcard SSL for both standard domains and subdomains.
In this article, I'm going to show you how to create a SSL Let's Encrypt certificate registration for your domain name and deploy it for Spring Boot application.
The instructions will be done on Ubuntu operating system because tools like openssl, and keytool are available here. However, you can work with Windows operating system if you install the those tools.
Although the SSL certificate provided by Let's Encrypt is free, but it has a very short validity period, namely 90 days, so every 90 days you have to re-create the SSL certificate. But thank God, the steps of re-creating the certificate are simple and don't take you much time.
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2- Registering SSL certificate

There are multiple ways to register a  Let's Encrypt certificate, but I highly recommend that you register at sslforfree.com. This website allows you to create an account with your email, and register an SSL certificate for your domain name. When you need to re-create a certificate, you just need a simple Click to download a new certificate with a validity period of 90 days.
First of all, on  sslforfree.com, enter your domain name and click  "Create Free SSL Certificate".
Then the  sslforfree website will ask you to sign up for an account:
Next, you have to verify that you are indeed the owner of that domain name, and declare information about your domain name, such as Your Country, City, Company Name, etc.
Finally, Let's Encrypt will allow you to download a ZIP file containing 3 files.
Note: For Web applications written in Java language, you need to select  Tomcat for the  "Server Type".
  1. certificate.crt: Certificate generated for your domain name.
  2. private.key: Private key of your certificate.
  3. ca_bundle.crt: Intermediate CA (Certificate Authority)

3- Converting to PKCS-12 format

Extract the ZIP file you have in the above step into a folder on Ubuntu. For example:
  • /home/{username}/mydomain.com
Java applications can read certificates when they are in  PKCS-12 (*.p12) format, so you have to convert the extracted files to this format.
openssl pkcs12 -export -in /home/tran/mydomain.com/certificate.crt -inkey /home/tran/mydomain.com/private.key -name mydomain -out /home/tran/mydomain.com/mydomain_com.p12


keytool -importkeystore -deststorepass YourPassword -destkeystore /home/tran/mydomain.com/mydomain_com.jks -srckeystore /home/tran/mydomain.com/mydomain_com.p12 -srcstoretype PKCS12
After executing the above two commands, you will have 2 new files as shown below:

4- Spring Boot Configuration

On the Spring Boot project, open the application.properties file to configure SSL.
application.properties
server.port=443

server.ssl.key-store=file:/home/tran/mydomain.com/mydomain_com.p12

server.ssl.key-store-password=YourPasswoord

server.ssl.key-alias=mydomain
Deploy your website and access it with HTTPS:
  • https://mydomain.com
Note: If you package the Spring Boot application as JAR (or WAR) and run it directly through COMMAND, you may not need to add anything to the  application.properties, just run the application like this:
java -jar mydomaintest-1.0.war --server.port=443 -Dserver.ssl.key-store=file:/home/tran/mydomain.com/mydomain_com.jks -Dserver.ssl.key-store-password=YourPassword -Dserver.ssl.key-alias=mydomain

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