InteractiveBrowserCredentialOptions.RedirectURL doesn't work

[chlowell]

InteractiveBrowserCredential.GetToken() starts a redirect server only when InteractiveBrowserCredentialOptions.RedirectURL has no value:

azure-sdk-for-go/sdk/azidentity/interactive_browser_credential.go

Lines 128 to 132 in 6ff9912

	redirectURL := opts.RedirectURL
	if redirectURL == "" {
	redirectURL = rs.Start(state.String(), opts.Port)
	}
	defer rs.Stop()

Acquiring a token is therefore impossible when the option has a value. Fixing this is more complex than simply ensuring the redirect server starts, because the server doesn't work for all valid values of RedirectURL, e.g. https://127.0.0.1. However, MSAL for Go supports RedirectURL, so this should be easy to fix as part of #14920.

[jhendrixMSFT]

Affects edge-cases, not a GA-blocker.

[chlowell]

Switching to MSAL's implementation will fix this for the common case. However, an application that has registered https://localhost but not http://localhost for a redirect URI (which is unusual) won't be able to authenticate users until AzureAD/microsoft-authentication-library-for-go#281 is fixed.