fix: sign redirect with secret from env var

[eduardoboucas]

Summary

Follow-up to #5414. The signed property holds the name of the environment variable that holds the secret for signing redirects. It does not hold the secret itself.

[github-actions]

📊 Benchmark results

Comparing with 027efcf

Package size: 267 MB

(no change)

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└───┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴────┴──┴──>
    T-12    T-11    T-10    T-9     T-8     T-7     T-6     T-5     T-4     T-3     T-2     T-1      T    

Legend

• T-16 (bce1f2c): 260 MB
• T-15 (2d3923c): 260 MB
• T-14 (6726bf4): 267 MB
• T-13 (87adddc): 267 MB
• T-12 (6d6531a): 267 MB
• T-11 (f33c595): 267 MB
• T-10 (6594da7): 267 MB
• T-9 (22ecec6): 260 MB
• T-8 (c7c5fff): 267 MB
• T-7 (7e27e7a): 267 MB
• T-6 (89754a1): 267 MB
• T-5 (2aa9341): 267 MB
• T-4 (734c23c): 267 MB
• T-3 (e978613): 267 MB
• T-2 (733c47e): 267 MB
• T-1 (027efcf): 267 MB
• T (current commit): 267 MB

[charliegroll]

oops misread - LGTM