Setup zeroizing secrets

[paolobarbolini]

Closes #30

[codecov]

Codecov Report

Merging #40 (4c0aab9) into main (036840b) will decrease coverage by 0.38%.
The diff coverage is 44.44%.

@@            Coverage Diff             @@
##             main      #40      +/-   ##
==========================================
- Coverage   91.92%   91.53%   -0.39%     
==========================================
  Files          26       26              
  Lines        1288     1300      +12     
==========================================
+ Hits         1184     1190       +6     
- Misses        104      110       +6     

Impacted Files	Coverage Δ
src/credentials/serde.rs	71.05% <16.66%> (-12.29%)	⬇️
src/credentials/mod.rs	97.72% <100.00%> (ø)
src/signing/signature.rs	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 036840b...4c0aab9. Read the comment docs.