Refactor authentication process and update tests accordingly

[gelleson]

Updated the authentication process in the ClientConfig by replacing the authToken string with AuthBuilder functions. This allows setting up various authentication headers, supporting different types of authentication like OpenAI or Azure AD. As part of this update, corresponding tests have also been modified to work with the new authentication process.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.46%. Comparing base (0925563) to head (7990f40).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #693   +/-   ##
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  Coverage   98.46%   98.46%           
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  Files          24       24           
  Lines        1366     1370    +4     
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+ Hits         1345     1349    +4     
  Misses         15       15           
  Partials        6        6           

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[sashabaranov]

@gelleson thank you for the PR! And sorry for taking so long for reviewing it — I think it's an important very area and should be treated appropriately.

In the context of #700 — do we maybe make this change more general, so different providers would handle API keys and specific URL formatting?

[sashabaranov]

I suggest we make it an interface with setAuthTokenForRequest func

[sashabaranov]

Considering #700, here's a sketch of how we can approach different API providers:

type apiProvider interface { // not exposing the provider type itself?
	SetAuthForRequest(req *http.Request)
	GetFullURL(suffix string, args ...any) // Shouldn't be `any`, but a type-safe list like requestOption
}

type APIProviderConfig interface {
	// whatever we need here
}

client usage:

config := openai.DefaultConfigWithAPIProvider(
	openai.AzureOpenAIProviderConfig("your Azure OpenAI Key", "https://your Azure OpenAI Endpoint"),
)
client := openai.NewClientWithConfig(config)