feat: add authentication default settings support

[yayami3]

Add authentication default settings support

Summary

This PR provides a comprehensive solution to issue #654 by adding configurable default authentication settings that eliminate repeated prompts during q login. This implementation supersedes PR #655 by not only supporting CLI arguments but also persistent default settings.

Motivation

Issue #654 reports that q login always prompts for start URL and region even when --identity-provider and --region are provided via CLI arguments. While PR #655 addresses the immediate CLI argument issue, users still face repeated prompts across login sessions.

This PR provides a more complete solution by:

1. ✅ Skipping prompts when CLI arguments are provided (addresses PR feat(cli): skip prompts when identity provider and region CLI args are provided (issue #654) #655)
2. ✅ Supporting persistent default settings for repeated use (goes beyond PR feat(cli): skip prompts when identity provider and region CLI args are provided (issue #654) #655)
3. ✅ Providing visual feedback when defaults are used
4. ✅ Auto-saving CLI arguments as defaults for future use

Changes

New Settings

Three new settings are introduced that users can configure via q settings:

• auth.defaultLicense: Default license type ("free" or "pro")
• auth.defaultRegion: Default AWS region (e.g., "us-east-1")
• auth.defaultIdentityProvider: Default Identity Center start URL

Behavior

Priority order (highest to lowest):

1. CLI arguments (e.g., --region us-east-1)
2. Explicit default settings (configured via q settings)
3. Previous values (shown as prompt defaults, requires Enter)

When CLI arguments or default settings exist, prompts are automatically skipped with visual feedback.

Example Usage

Scenario 1: Using CLI arguments (PR #655 behavior)

q login --license pro --identity-provider "https://example.awsapps.com/start" --region us-east-1
# ✅ No prompts - uses CLI arguments directly
# ✅ These values are saved as defaults for next time

Scenario 2: Using persistent defaults (NEW)

# One-time configuration
q settings auth.defaultLicense "pro"
q settings auth.defaultRegion "us-east-1"
q settings auth.defaultIdentityProvider "https://example.awsapps.com/start"

# Future logins automatically use these defaults
q login
# Output:
# Using license: Pro (Identity Center)
# Using Start URL: https://example.awsapps.com/start
# Using Region: us-east-1
# [authentication flow continues without prompts...]

Scenario 3: Override defaults with CLI arguments

q login --region us-west-2  # Overrides default region
# Using license: Pro (Identity Center)
# Using Start URL: https://example.awsapps.com/start
# Using Region: us-west-2  ← CLI argument takes precedence
# ✅ us-west-2 is now saved as the new default

Scenario 4: First-time setup with CLI arguments

# First login with CLI arguments
q login --license pro --region us-east-1 --identity-provider "https://example.awsapps.com/start"
# ✅ Values are automatically saved as defaults

# Subsequent logins are simpler
q login
# ✅ Uses saved defaults, no prompts needed

Implementation Details

• Added resolve_auth_value() helper function to handle priority resolution
• Modified login_interactive() to check CLI args → default settings → prompt
• CLI arguments are automatically saved as default settings after successful authentication
• Visual feedback shows which values are being used
• Maintains backward compatibility - existing behavior unchanged when no defaults are configured

Comparison with PR #655

Feature	PR #655	This PR
Skip prompts with CLI args	✅	✅
Persistent default settings	❌	✅
Visual feedback	❌	✅
Auto-save CLI args as defaults	❌	✅
License type defaults	❌	✅
Automation-friendly	✅	✅
User-friendly for repeated use	❌	✅

Testing

• ✅ Build successful
• ✅ Existing tests pass (except 1 pre-existing environment-specific test failure)
• ✅ Manual testing confirms:
  • CLI arguments skip prompts (PR feat(cli): skip prompts when identity provider and region CLI args are provided (issue #654) #655 behavior)
  • Default settings skip prompts (new behavior)
  • Priority order works correctly
  • CLI arguments are saved as defaults after login

Related Issues

• Closes bug: q login always prompts for start url and region even if the --identity-provider and --region are provided #654
• Supersedes feat(cli): skip prompts when identity provider and region CLI args are provided (issue #654) #655 (provides more comprehensive solution)
• Parallel to amazon-q-developer-cli#2659 and #2660