Adding multi certificate validation

[nilasini]

Proposed changes in this pull request

Reolves https://github.com/wso2/product-is/issues/3295 Added back the reverted PR https://github.com/wso2-extensions/identity-outbound-auth-samlsso/pull/67

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When should this PR be merged

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Follow up actions

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Checklist (for reviewing)

General

• [ ] Is this PR explained thoroughly? All code changes must be accounted for in the PR description.
• [ ] Is the PR labeled correctly?

Functionality

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• [ ] Does the UI work as expected? There should be no Javascript errors in the console; all resources should load. There should be no unexpected errors. Deliberately try to break the feature to find out if there are corner cases that are not handled.

Code

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• [ ] Does the PR introduce any inefficient database requests? Use the debug server to check for duplicate requests.
• [ ] Are all necessary strings marked for translation? All strings that are exposed to users via the UI must be marked for translation.

Tests

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• [ ] If this is a bug fix, are tests for the issue in place? There must be a test case for the bug to ensure the issue won’t regress. Make sure that the tests break without the new code to fix the issue.
• [ ] If this is a new feature or a significant change to an existing feature? has the manual testing spreadsheet been updated with instructions for manual testing?

Security

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• [ ] Does all branching logic have a default case?
• [ ] Does this solution handle outliers and edge cases gracefully?
• [ ] Are all external communications secured and restricted to SSL?

Documentation

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• [ ] Are changes to the API documented in the API docs? If this PR introduces new API functionality or changes existing ones, the changes must be documented.
• [ ] Are reusable components documented? If this PR introduces components that are relevant to other developers (for instance a mixin for a view or a generic form) they should be documented in the Wiki.