How to export credentials from one jenkins instance to another?

UPDATE: TL;DR Follow the link provided below in a comment by Filip Stachowiak it is the easiest way to do it. In case it doesn't work for you go on reading.

Copying the $HUDSON_HOME/credentials.xml is not the solution because Jenkins encrypts paswords and these can't be decrypted by another instance unless both share a common key.

So, either you use the same encription keys in both Jenkins instances (Where's the encryption key stored in Jenkins? ) or what you can do is:

1. Create the same user/password, you need to share, in the 2nd Jenkins instance so that a valid password is generated

2. What is really important is that user ids in both credentials.xml are the same. For that (see the credentials.xml example below) for user: Jenkins the identifier <id>c4855f57-5107-4b69-97fd-298e56a9977d</id> must be the same in both credentials.xml

   <com.cloudbees.plugins.credentials.SystemCredentialsProvider plugin="[email protected]">
     <domainCredentialsMap class="hudson.util.CopyOnWriteMap$Hash">
       <entry>
         <com.cloudbees.plugins.credentials.domains.Domain>
           <specifications/>
         </com.cloudbees.plugins.credentials.domains.Domain>
         <java.util.concurrent.CopyOnWriteArrayList>                
           <com.cloudbees.plugins.credentials.impl.UsernamePasswordCredentialsImpl>
             <scope>GLOBAL</scope>
             <id>c4855f57-5107-4b69-97fd-298e56a9977d</id>
             <description>Para SVN</description>
             <username>jenkins</username>
             <password>J1ztA2vSXHbm60k5PjLl5jg70ZooSFKF+kRAo08UVts=    
             </password>                        
           </com.cloudbees.plugins.credentials.impl.UsernamePasswordCredentialsImpl>
         </java.util.concurrent.CopyOnWriteArrayList>
       </entry>
     </domainCredentialsMap>
   </com.cloudbees.plugins.credentials.SystemCredentialsProvider>
   

I was also facing the same problem. What worked for me is I copied the credentials.xml, config.xml and the secrets folder from existing jenkins to the new instance. After the restart of jenkins things worked fine.