Sounds like the REST endpoint you are connecting to is presenting a  Certificate that is not trusted by your PRPC system (or possibly [rarer] it is requesting that your REST call present it's own Client Certificate [two-way SSL]).

First find out if you are using TWO-WAY SSL (because that involves more steps); if you are not and are just using ONE-WAY SSL; then see below for a general approach about what you probably need to do here.

SUGGESTED STEPS:

1. Use 'openssl' to retrieve the certificate used by the endpoint.

Like this:

openssl s_client -connect www.google.com:443 -showcerts

If you look through the output, you'll see at least one Certificate (base64 encoded, PEM format); so in the example above; I get this Certificate (actually I get three in total - but here's the last one in the list for illustration):

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

If you take this text (including the 'BEGIN/END' lines) and save it in a file with the extension 'cer' Windows will automatically read this as a Certificate file:

If you are running on a Linux Platform, you should have 'openssl' available by default, if you are Windows, you'll need to install it.

-or-

2. Use a browser to attach to the REST endpoint directly:

So ; this is just 'google.co.uk' viewed in Chrome - The Endpoint NOT a REST endpoint (but that doesn't matter here).

Click on the padlock:

Then 'Security | View Certificate':

NOTE: if you get a Certificate error when you access the REST endpoint : this (probably) indicates that the REST Endpoint is not using a CA-Signed Certificate, but instead using a Self-Signed Certificate.

If the Endpoint is using a Self-Signed Certificate (or even a 'Corporate CA Signed Certificate); then your browser - and more importantly Java will not trust the Certificate; and will refuse to complete the SSL connection.

To inform Java (well in this case more specifically PRPC) to trust the endpoint's Certificate - you need to include it (or more likely the signing Certificate) in a Java Truststore (confusingly called a 'keystore' in the general sense, even though it doesn't necessarily include any key-pairs).

For Java in general: you would import the Certificate in the Java file:

JAVA_HOME\jre\lib\security\cacerts

 

You use the JDK 'keytool' for this: see here for an example : http://stackoverflow.com/questions/4325263/how-to-import-a-cer-certificate-into-a-java-keystore

For PRPC - you create a 'Keystore Rule' and reference it from your Connector (depending on your version of PRPC; you may need to do this at 'CACERTS' level).