Add CSEK decryption for storage.get(BlobId,..)

[frankyn]

Hi @JesseLovelace,

Could you take a look at this fix for an internal customer request: b/79339975.

Currently storage.get() doesn't support decrypting object crc32c and md5 using CSEK. When objects are encrypted using CSEK, md5 and crc32c are also encrypted. Without supporting the option to decrypt it blocks this specific use-case.

For more information: https://cloud.google.com/storage/docs/encryption/customer-supplied-keys#encrypted-elements

[codecov]

Codecov Report

Merging #5882 into master will increase coverage by <.01%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master    #5882      +/-   ##
============================================
+ Coverage     46.79%   46.79%   +<.01%     
- Complexity    25648    25663      +15     
============================================
  Files          2456     2456              
  Lines        267593   267596       +3     
  Branches      30564    30559       -5     
============================================
+ Hits         125225   125228       +3     
  Misses       133109   133109              
  Partials       9259     9259

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/com/google/cloud/storage/Storage.java	85.07% <0%> (-0.77%)	0 <0> (ø)
...e/src/main/java/com/google/cloud/storage/Blob.java	81.59% <0%> (-0.51%)	30 <0> (ø)
...om/google/cloud/storage/spi/v1/HttpStorageRpc.java	1.81% <0%> (ø)	1 <0> (ø)	⬇️
...gflow/v2beta1/stub/KnowledgeBasesStubSettings.java	80.3% <0%> (ø)	15% <0%> (ø)	⬇️
...google/cloud/vision/v1/ImageAnnotatorSettings.java	17.07% <0%> (ø)	2% <0%> (ø)	⬇️
.../dialogflow/v2beta1/stub/ContextsStubSettings.java	80.57% <0%> (ø)	16% <0%> (ø)	⬇️
...stub/GameServerDeploymentsServiceStubSettings.java	88.06% <0%> (ø)	27% <0%> (ø)	⬇️
...le/cloud/gaming/v1alpha/RealmsServiceSettings.java	16.27% <0%> (ø)	2% <0%> (ø)	⬇️
...cloud/vision/v1p4beta1/ImageAnnotatorSettings.java	17.07% <0%> (ø)	2% <0%> (ø)	⬇️
...alogflow/v2beta1/stub/EntityTypesStubSettings.java	87.22% <0%> (ø)	25% <0%> (ø)	⬇️
... and 78 more

---

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 123d374...d5af46f. Read the comment docs.

[frankyn]

Thanks @JesseLovelace!