Describe the bug
We are running behind a proxy. Attempt to install STS4 on Eclipse 2021-03 fails with error:
Unable to read repository at https://download.springsource.com/release/TOOLS/sts4/update/e4.19/content.xml.
PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

To Reproduce

1. Start Eclipse 2021-03
2. Menu > Help > Eclipse Marketplace
3. Search for "Springboot tools suite"
4. Select SpringTools Suite 4 (aka Spring Tools Suite 4) 4.10.0.RELEASE
5. Click on Install button
6. "Confirm Selected Feature" popup shows listing STS4 features that will be installed, all are selected
7. Click on "Confirm>" button

This results in the above error.

I have 2 versions of JDK installed on my system in C:\Program Files\Java

• jdk1.8.0_172 -> This one is set in Environment Variables System Path variable as JAVA_HOME
• jdk-11.0.10

Following accepted answer instructions on this Stackoverflow https://stackoverflow.com/questions/21076179/pkix-path-building-failed-and-unable-to-find-valid-certification-path-to-requ, I:

• navigated to https://marketplace.eclipse.org/content/spring-tools-4-aka-spring-tool-suite-4 (also tried http instead of https, both resulting in the same error above)
• exported certificate to a file
• added certificate using keytool
• confirmed that it was added using keytool to list certificates
• restarted my machine
• tried the same steps as described above by starting eclipse > Help > Eclipse Marketplace...

But adding certificate did not help, I am getting still the same error.

Also, If I go to eclipse market place website () and click the orange download button below STS to open "Update Site URL" box and copy the URL where it says "Add this URL to your Eclipse Installation to reach this solution's update site. 2021-03 (4.19)" into browser, I get following error:

<Error>
<Code>AccessDenied</Code>
<Message>Access Denied</Message>
<RequestId>RM671CKBEYD78Y12</RequestId>
<HostId>H91VMFfnoo/MXxns6iPpxoO3N2Zz4ATPUEfBlkAxH34ocbBa6Sa0pGudUqn4gAE5gSScEQWydVU=</HostId>
</Error>

Sample
non-applicable