refactor: make credentials.NewMemoryStore return an interface

[Wwwsylvia]

1. Un-expose credentials.MemoryStore as it is unecessary to be public
2. Make credentials.NewMemoryStore return an interface instead of a struct

[codecov-commenter]

Codecov Report

Merging #605 (0a6db83) into main (9f83e67) will decrease coverage by 0.19%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main     #605      +/-   ##
==========================================
- Coverage   74.64%   74.45%   -0.19%     
==========================================
  Files          59       59              
  Lines        5266     5266              
==========================================
- Hits         3931     3921      -10     
- Misses        983      991       +8     
- Partials      352      354       +2     

Files Changed	Coverage Δ
registry/remote/credentials/memory_store.go	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[Wwwsylvia]

@uanid Please take a look at this change

[shizhMSFT]

LGTM

[uanid]

@uanid Please take a look at this change

How about changing FileStore to a private too?
If we add the DisablePut property to NewFileStore? Then, we could make it private.
Changing the public API could be an issue, but since you moved the code to oras-go and package path is changed, some changes now seem okay.

[TerryHowe]

@uanid Please take a look at this change

How about changing FileStore to a private too? If we add the DisablePut property to NewFileStore? Then, we could make it private. Changing the public API could be an issue, but since you moved the code to oras-go and package path is changed, some changes now seem okay.

Sounds like a good idea, but subject of another PR, although I don't know if it is practical.

[TerryHowe]

/lgtm

[uanid]

@uanid Please take a look at this change

LGTM too

[Wwwsylvia]

How about changing FileStore to a private too?
If we add the DisablePut property to NewFileStore? Then, we could make it private.
Changing the public API could be an issue, but since you moved the code to oras-go and package path is changed, some changes now seem okay.

But that would require users to specify an extra parameter on initialization. I think it's ok to keep FileStore exposed for convenience. @shizhMSFT What do you think?

[shizhMSFT]

But that would require users to specify an extra parameter on initialization. I think it's ok to keep FileStore exposed for convenience.

The point of having FileStore exposed is to make the property changeable after initialization.