[GDS Client] Fix Certificate Request when private Key of existing Certificate is not exportable

[romanett]

Proposed changes

The GDS Client uses a Certificate Signing Request (CSR) when a new CA signed Certificate is requested from the GDS and an older cert exists.

The CSR can be executed however applying the existing private key to the new Certificate fails when the old Certificates private Key is not exportable. This is the case e.g. for many certs in the Windows X509 Certificate Store.

With this fix the GDS Client uses a KeyPair Request instead of a Certificate Signing Request to request a new CA signed Cert from the GDS, when the private key of the existing cert is not exportable.

Related Issues

• Fixes #606

Types of changes

• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] Enhancement (non-breaking change which adds functionality)
• [ ] Test enhancement (non-breaking change to increase test coverage)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected, requires version increase of Nuget packages)
• [ ] Documentation Update (if none of the other choices apply)

Checklist

• [x] I have read the CONTRIBUTING doc.
• [x] I have signed the CLA.
• [ ] I ran tests locally with my changes, all passed.
• [ ] I fixed all failing tests in the CI pipelines.
• [ ] I fixed all introduced issues with CodeQL and LGTM.
• [ ] I have added tests that prove my fix is effective or that my feature works and increased code coverage.
• [ ] I have added necessary documentation (if appropriate).
• [ ] Any dependent changes have been merged and published in downstream modules.

Further comments