Add signature file for VBA projects

[HolgiHo]

PR for issue #411.

Library changes:

• workbook: new API function workbook_add_vba_project_signature
• packager: copy vbaProjectSignature.bin, create vbaProject.bin.rels

Tests:

• new functional test test_macro_signed

Examples:

• add examples/macro_signed.c
• fix examples/vbaProject.bin: Was corrupted; now the button press works again; VBA project is signed by "VBA Code Signing"
• add examples/vbaProjectSignature.bin: The digitial signature, based on "VBA Code Signing" certificate

Utilities for testing the VBA project is signed correctly:

• new directory dev/vba_code_signing containing:
  • the "VBA Code Signing" certificate certificate.pfx that was used to sign the VBA project file. This certificate is self-signed and only for testing purposes. The private key is "xlsxwriter". In reality, you would obtain a code signing certificate from an offical Certificate Authority. This process is usually quite complex and expensive.
  • PowerShell scripts for creating, exporting, and importing VBA code signing certificates. Execute import_certificate.ps1 to install certificate.pfx on your computer to test the example VBA project is actually signed in Excel.

[HolgiHo]

Will open another PR with some fixes.

[jmcnamara]

Thanks for that. It was only requested once but I think it is a useful feature. Some comments.

• workbook: new API function workbook_add_vba_project_signature

I think a better function name would be workbook_add_signed_vba_project_signature(lxw_workbook *self, const char *vba_project, const char *signature).

It could call workbook_add_vba_project() internally to add the vba macros/project.

packager: copy vbaProjectSignature.bin, create vbaProject.bin.rels

Ok.

new functional test test_macro_signed

Good. But you could just call it test_macro04.

add examples/macro_signed.c

You can omit the example. It isn't common enough or complicated enough to need one.

fix examples/vbaProject.bin: Was corrupted; now the button press works again;

I haven't had any report that it is corrupted and I just tested it again and it seems to work fine. So you can omit this change (or figure out if it is a Windows issue).

Utilities for testing the VBA project is signed correctly:

Ok.

I'll make other comments inline if needed.

[HolgiHo]

I think a better function name would be workbook_add_signed_vba_project_signature(lxw_workbook *self, const char *vba_project, const char *signature).

Do you mean workbook_add_signed_vba_project (without "signature)?

It could call workbook_add_vba_project() internally to add the vba macros/project.

Ok.

fix examples/vbaProject.bin: Was corrupted; now the button press works again; I will double-check.

Please check out PR #415 as I have fixed the git commit message there.