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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[sellakumaran]

Doc says 0x236496A2 (593742242 decimal). Actual conversion is 593794722. Replace 593742242 with 593794722. (PR description body already has the correct value.)

[sellakumaran]

The existing AuthenticationConstantsTests only asserts the literal string values of the two constants — the matcher that gates the fallback branch has no direct coverage.

Change private static → internal static on the helper (InternalsVisibleTo for the test project is already in Microsoft.Agents.A365.DevTools.Cli.csproj:22, no csproj edit needed). Cover:

• Both strings present, exact case → true
• Both strings present, mixed case → true (validates OrdinalIgnoreCase)
• Only ApiContractViolation present → false
• Only "declined scopes are present" → false
• Neither present → false
• Verbatim live WAM error message from the PR's test plan run → true (pins the matcher to MSAL's actual output so a future MSAL reword fails this test instead of silently regressing live behavior)

[sellakumaran]

WAM is Windows-only (MsalBrowserCredential.cs:386,418-426 — if (_useWam) vs. "System browser on Mac/Linux"). On macOS/Linux there is no WAM to bypass.

Either:

• Drop the parenthetical: Authentication mode: device code
• Append (WAM bypassed) only when OperatingSystem.IsWindows()

[sellakumaran]

1. Change _logger?.LogWarning(...) → _logger?.LogInformation(...). The branch is a successful auto-recovery on the documented, intended path — the message itself says "This is expected for Exchange-specific Graph scopes". Warning level for an expected event is noise.
2. Append a hint to the message: "Tip: pass --device-code on subsequent runs to skip the WAM probe." so users discover the flag the first time they hit the fallback.

[sellakumaran]

The if (deviceCode) logger.LogInformation("Authentication mode: device code (WAM bypassed)") line lives inside the explicit-scopes branch. The manifest branch (line 217 / AcquireAndDisplayManifestTokensAsync) routes deviceCode through but never logs it.

Move the if (deviceCode) logger.LogInformation(...) up to immediately after var deviceCode = ... is read so it fires for both branches.

[sellakumaran]

Called once in the catch (...) when (...) filter (line 462) and again in the body (line 476). Hoist bool isDeclined = IsWamDeclinedScopesError(ex); at the top of the catch body and reuse it.