[JENKINS-74964] Display error message when adding invalid certificate credentials

[Priya-CB]

JENKINS-74964

• The "Add Credentials" popup now correctly displays an error message when users attempt to add invalid certificate credentials. Previously, the validation errors were shown on the form but no error message appeared upon clicking "Add," leading to a silent rejection of the credentials.

Testing done

Automated Unit Testing

Implemented unit tests to verify that the error messages are returned in the response on form submit

Manual Testing

1. Adding certificate credentials with invalid inputs (e.g., empty PEM-encoded certificates or password < 14 characters in FIPS mode).
2. Verified that clicking "Add" prevents invalid credentials from being stored and displays an appropriate error message to the user.

Popup screen:

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[Priya-CB]

"Add Credentials" popup does not handle HTML responses ("angry Jenkins"), causing the catch block to execute. Added notificationBar to inform the user about the failure(unexpected cases) in credential creation.

[fcojfernandez]

AFAIK FormException is not a RuntimeException, and only `RuntimeException are not causing a LinkageError: https://github.com/jenkinsci/jenkins/blob/171097618b5b2b70ec3142e3efc80b4f2aff9601/core/src/main/java/hudson/model/Descriptor.java#L623 so

Suggested change

	* Descriptor#newInstanceImpl throws a LinkageError if the constructor throws any exception other
	* than HTTP response exceptions such as Descriptor.FormException.
	* Descriptor#newInstanceImpl throws a LinkageError if the DataBoundConstructor or any DataBoundSetter throw any exception other
	* than RuntimeException implementing HttpResponse.

[Priya-CB]

While FormException itself is not a RuntimeException, it is wrapped into HttpResponses, which is a RuntimeException,
https://github.com/jenkinsci/stapler/blob/master/core/src/main/java/org/kohsuke/stapler/RequestImpl.java#L691

[fcojfernandez]

no, that's incorrect. As for https://github.com/jenkinsci/jenkins/blob/171097618b5b2b70ec3142e3efc80b4f2aff9601/core/src/main/java/hudson/model/Descriptor.java#L622-L627 the Linkage error only can happen if the caught exception is RuntimeException AND HttpResponse. FormException is not in the catch clause, so it's not caught at all but directly thrown as stated in the method signature. The only way of getting a LinkageError is that the error is a NoSuchMethodException, an InstantiationException, an IllegalAccessException, an InvocationTargetException, or a RuntimeException that is not implementing HttpResponse

[Priya-CB]

You are correct that FormException is not explicitly in the catch clause of Descriptor#newInstanceImpl. However, my point was that FormException, when thrown, is wrapped into HttpResponses and HttpResponses is a RuntimeException.
Because of this wrapping, it ultimately satisfies the condition of being a RuntimeException and implementing HttpResponse

[Priya-CB]

Updated the comment

[jmdesprez]

I agree with previous reviews/comments