feat(get-token): add --device-code flag and auto-fallback for Exchange Graph scopes

[lwokeray]

Summary

• Adds --device-code flag to a365 develop get-token so users can bypass WAM for Exchange-specific Graph scopes that WAM rejects
• Extends MsalBrowserCredential to automatically detect WAM ApiContractViolation + "declined scopes are present" errors and fall back to device code, rather than throwing
• Adds two new constants (WamDeclinedScopesError, WamApiContractViolation) to AuthenticationConstants to document and centralize the known WAM error signatures

Background

WAM (Windows Account Manager) rejects Exchange-specific Microsoft Graph scopes such as MailboxSettings.ReadWrite and ExchangeMessageTrace.Read.All with an ApiContractViolation error containing "declined scopes are present". This internal error code (593794722 decimal) does not begin with 0xcaa, so the existing WAM fallback logic in MsalBrowserCredential does not trigger — the exception is rethrown and the user sees an unhelpful MSAL error.

Changes

AuthenticationConstants.cs

• WamDeclinedScopesError = "declined scopes are present" — substring matched against WAM ApiContractViolation messages
• WamApiContractViolation = "ApiContractViolation" — the WAM error classification that accompanies declined scopes

MsalBrowserCredential.cs

• Added IsWamDeclinedScopesError(MsalException) private static helper — returns true when both WAM error strings are present in the exception message
• Extended the WAM catch clause to also catch declined-scopes errors via || IsWamDeclinedScopesError(ex)
• Added a targeted fallback branch that logs a descriptive warning and delegates to AcquireTokenWithDeviceCodeFallbackAsync, so Exchange-scope requests automatically retry via device code without user intervention

GetTokenSubcommand.cs

• Added --device-code option (bool, default false) with description explaining WAM limitation and Exchange scope use-case
• Propagated the flag through AcquireAndDisplayTokenAsync, AcquireAndDisplayManifestTokensAsync, and AcquireTokenAsync
• AcquireTokenAsync passes useInteractiveBrowser: !useDeviceCode to AuthenticationService.GetAccessTokenWithScopesAsync

Tests

• GetTokenSubcommandTests.cs: added CreateCommand_ShouldHaveDeviceCodeOption, CreateCommand_DeviceCodeOption_DescriptionShouldMentionExchangeScopes; updated CreateCommand_ShouldHaveAllRequiredOptions (count 8 → 9)
• AuthenticationConstantsTests.cs: added WamDeclinedScopesError_ShouldMatchKnownWamErrorSubstring, WamApiContractViolation_ShouldMatchKnownWamErrorClassification, WamDeclinedScopesError_ShouldBeDifferentFromWamConsentRequiredError

Test plan

• dotnet build dirs.proj --configuration Release — 0 errors, 0 warnings
• dotnet test tests.proj --configuration Release — all 90 tests pass
• Live test: a365 develop get-token --resource-id 00000003-0000-0000-c000-000000000000 --scopes "MailboxSettings.ReadWrite ExchangeMessageTrace.Read.All" --device-code — prompts with device code URL, acquires token successfully
• Without --device-code on a machine where WAM rejects Exchange scopes: confirm automatic fallback warning appears and device code flow is used

🤖 Generated with Claude Code

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