fix(auth): allow prompt=none silent SSO to resume federated sessions (#14897)

[soberm]

Description of changes

With options: { prompt: 'NONE' }, signInWithRedirect still appended identity_provider=COGNITO to the authorize request. Cognito treats that parameter as a provider selector, so a live hosted UI session that came from a federated IdP (for example Google or SAML) was not resumed and Cognito returned error=login_required.

identity_provider is now omitted when prompt is NONE and neither provider nor idpIdentifier is specified, letting Cognito resume whichever session is already active. Interactive behavior is unchanged (a no-argument call still sends identity_provider=COGNITO), and there is no public API change.

Issue #, if available

Fixes #14897

Description of how you validated changes

Added unit tests covering the silent SSO path and the unchanged explicit-provider, idpIdentifier, and non-NONE prompt paths; the full packages/auth suite (1150 tests) and the build pass.

Checklist

• PR description included
• yarn test passes
• Unit Tests are changed or added

Checklist for repo maintainers

• Verify E2E tests for existing workflows are working as expected or add E2E tests for newly added workflows
• New source file paths included in this PR have been added to CODEOWNERS, if appropriate

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[changeset-bot]

🦋 Changeset detected

Latest commit: cca5a07

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@aws-amplify/auth	Patch
@aws-amplify/pubsub	Patch
aws-amplify	Patch

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