You need to add the certificate for App2 to the truststore file of the used JVM located at $JAVA_HOME\lib\security\cacerts.
First you can check if your certificate is already in the truststore by running the following command:
keytool -list -keystore "$JAVA_HOME/jre/lib/security/cacerts" (you don’t need to provide a password)
If your certificate is missing, you can get it by downloading it with your browser and add it to the truststore with the following command:
keytool -import -noprompt -trustcacerts -alias <AliasName> -file <certificate> -keystore <KeystoreFile> -storepass <Password>
Example:
keytool -import -noprompt -trustcacerts -alias myFancyAlias -file /path/to/my/cert/myCert.cer -keystore /path/to/my/jdk/jre/lib/security/cacerts/keystore.jks -storepass changeit
After import you can run the first command again to check if your certificate was added.
Sun/Oracle information can be found here.