removed XML declaration before signature operations

[call-stack]

Overview/Description

In this merge request, I have implemented a change to the process of generating and validating XML signatures. Specifically, I've removed the XML declaration from documents before these cryptographic operations are performed.

Why the Change Was Necessary

The presence of an XML declaration was found to potentially affect the consistency of the signature generation and validation processes. Differences in the XML prolog presence could lead to mismatches in signature validation, which in turn could compromise the integrity and reliability of the system.

What Was Changed

• XML Parsing Adjustment: The code now systematically removes the XML declaration from the document before any signature-related processing occurs. This ensures that the XML content fed into the signing and validation processes is consistent, regardless of its original state.
• Code Refactoring: Minor refactoring was done to enhance the clarity and efficiency of the signature processing functions, aligning with best practices for XML manipulation.

Impact of the Change

This change standardizes how XML documents are handled, removing potential discrepancies that could arise from varying XML prolog presence. As a result, the system's cryptographic operations are now more robust and less prone to errors related to XML formatting differences.

Additional Notes

• Testing: tests were added to validate xml signature digest with signature digest generate using xmlsec

[adamdecaf]

@call-stack Thanks for the PR! It looks like there's a small typo to fix.

[call-stack]

Thanks for fixing the typo.
I had moved this PR to Draft state.
Reason: when we are calling doc.RemoveChild(p) it is keeping the empty line there. I raised it here but the solution provided seems to be changing indentation. Fixed with the new commit.
Etree issue

[adamdecaf]

Thank you for this improvement!