Locally reproducable release source archives
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### Problem to solve
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As maintainer of a project i want to upload signatures to the source archives created by gitlab for a release. For this the commands/algorithms used to create the archives by gitlab must be locally reproducable.
### Further details
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I don't think it's smart to blindly download the generated archives and upload signatures for them since that wouldn't protect against servers that have been compromised.
### Proposal
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Provide documentation for tar/zip command flags that will allow maintainers to reproduce the the source archives locally.
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