diff --git a/CHANGELOG.md b/CHANGELOG.md
index fbbbaea..528c7c0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,29 @@
 
 ### Security
 
+- **OIDC provider "Test connection" panel (Audit 2026-05-11 Fix 09 — MED-5 GUI half).**
+  MED-5's backend dry-run endpoint (`POST /api/v1/auth/oidc/test`, gated
+  `auth.oidc.create`) shipped on `dev/auth-bundle-2` but had no GUI caller —
+  the `authOIDCTestProvider` function in `web/src/api/client.ts` was dead
+  code. Operators had to complete the create form blind, save, then click
+  "Refresh" to discover whether the issuer URL worked; failures left a
+  broken provider row in the database that had to be deleted before
+  retrying. New shared component
+  `web/src/pages/auth/OIDCTestConnectionPanel.tsx` calls the backend
+  against the live form state and renders a four-row status panel inline:
+  Discovery fetched, JWKS reachable, supported algs (warns when the IdP
+  advertises none), and RFC 9207 iss-parameter advertisement (informational
+  `·` glyph, not ✗, because the spec is SHOULD). Backend per-leg `errors[]`
+  flow into an inline bullet list. The panel is mounted in the
+  OIDCProvidersPage create modal AND the OIDCProviderDetailPage edit form —
+  the edit-form half is load-bearing for verifying IdP rotations (Keycloak
+  realm rename, Okta tenant move) without committing first. Run button is
+  disabled until the issuer URL is non-empty (whitespace-trimmed); the
+  component is read-only — safe to run repeatedly. 8 Vitest tests pin the
+  glyph-vs-glyph contract (✓/✗/⚠/·), the button-disabled-without-issuer
+  shape, and the test-id-suffix collision-prevention when the panel is
+  mounted twice on the same page.
+
 - **Scope-aware actor-role revoke (Audit 2026-05-11 A-4).**
   HIGH-10 made it possible to grant the same role to the same actor at
   multiple scopes (e.g. `r-operator` on `profile=p-acme` AND `profile=p-globex`)
diff --git a/web/src/pages/auth/OIDCProviderDetailPage.tsx b/web/src/pages/auth/OIDCProviderDetailPage.tsx
index 2bef966..da96d85 100644
--- a/web/src/pages/auth/OIDCProviderDetailPage.tsx
+++ b/web/src/pages/auth/OIDCProviderDetailPage.tsx
@@ -12,6 +12,7 @@ import { useAuthMe } from '../../hooks/useAuthMe';
 import PageHeader from '../../components/PageHeader';
 import ErrorState from '../../components/ErrorState';
 import { validateEmailDomain } from './OIDCProvidersPage';
+import OIDCTestConnectionPanel from './OIDCTestConnectionPanel';
 
 // =============================================================================
 // Bundle 2 Phase 8 — OIDCProviderDetailPage.
@@ -623,6 +624,17 @@ export default function OIDCProviderDetailPage() {
           )}
           {editing && (
             <>
+              {/* Audit 2026-05-11 Fix 09 — Test Connection panel (MED-5 GUI half).
+                  Lets the operator verify an issuer URL change post-rotation
+                  (e.g. Keycloak realm rename, Okta tenant move) without
+                  committing first. Reads from the live edit state so the
+                  scope of the test matches what Save would persist. */}
+              <OIDCTestConnectionPanel
+                issuerURL={editIssuerURL}
+                clientID={editClientID}
+                scopes={editScopesInput.split(/\s+/).filter(Boolean)}
+                testIDSuffix="edit"
+              />
               <button
                 onClick={saveEdit}
                 disabled={submitting}
diff --git a/web/src/pages/auth/OIDCProvidersPage.tsx b/web/src/pages/auth/OIDCProvidersPage.tsx
index e680186..8245c04 100644
--- a/web/src/pages/auth/OIDCProvidersPage.tsx
+++ b/web/src/pages/auth/OIDCProvidersPage.tsx
@@ -10,6 +10,7 @@ import {
 import { useAuthMe } from '../../hooks/useAuthMe';
 import PageHeader from '../../components/PageHeader';
 import ErrorState from '../../components/ErrorState';
+import OIDCTestConnectionPanel from './OIDCTestConnectionPanel';
 
 // =============================================================================
 // Bundle 2 Phase 8 — OIDCProvidersPage.
@@ -313,6 +314,16 @@ function CreateProviderModal({ isOpen, onClose, onSuccess }: CreateProviderModal
               </p>
             )}
           </div>
+          {/* Audit 2026-05-11 Fix 09 — Test Connection panel (MED-5 GUI half).
+              Dry-run the issuer URL + JWKS reachability + alg-downgrade defense
+              against MED-5's POST /api/v1/auth/oidc/test. Renders inline so the
+              operator sees the result before committing. */}
+          <OIDCTestConnectionPanel
+            issuerURL={form.issuer_url}
+            clientID={form.client_id}
+            scopes={form.scopes || []}
+            testIDSuffix="create"
+          />
           <div className="flex justify-end gap-2 pt-3">
             <button
               type="button"
diff --git a/web/src/pages/auth/OIDCTestConnectionPanel.test.tsx b/web/src/pages/auth/OIDCTestConnectionPanel.test.tsx
new file mode 100644
index 0000000..69bb527
--- /dev/null
+++ b/web/src/pages/auth/OIDCTestConnectionPanel.test.tsx
@@ -0,0 +1,218 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { render, screen, fireEvent, waitFor, cleanup } from '@testing-library/react';
+import OIDCTestConnectionPanel from './OIDCTestConnectionPanel';
+
+// Audit 2026-05-11 Fix 09 — OIDCTestConnectionPanel regression coverage.
+// Mocks authOIDCTestProvider so the test is hermetic (no real network).
+// Pins: button-disabled-without-issuer, happy-path renders all checks
+// green, failure-path renders the errors list, iss_param_supported=false
+// renders the informational `·` glyph rather than ✗ (since RFC 9207 is
+// SHOULD, not MUST).
+
+vi.mock('../../api/client', () => ({
+  authOIDCTestProvider: vi.fn(),
+}));
+
+import * as client from '../../api/client';
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  cleanup();
+});
+
+describe('OIDCTestConnectionPanel', () => {
+  it('RunButton — disabled until issuer URL is non-empty', () => {
+    render(<OIDCTestConnectionPanel issuerURL="" clientID="cid" scopes={['openid']} />);
+    const btn = screen.getByTestId('oidc-test-connection-run-default') as HTMLButtonElement;
+    expect(btn.disabled).toBe(true);
+  });
+
+  it('RunButton — enabled when issuer URL is non-empty', () => {
+    render(
+      <OIDCTestConnectionPanel
+        issuerURL="https://idp.example.com"
+        clientID="cid"
+        scopes={['openid']}
+      />,
+    );
+    const btn = screen.getByTestId('oidc-test-connection-run-default') as HTMLButtonElement;
+    expect(btn.disabled).toBe(false);
+  });
+
+  it('RunButton — also disabled when issuer URL is whitespace-only', () => {
+    render(<OIDCTestConnectionPanel issuerURL="   " clientID="cid" scopes={[]} />);
+    const btn = screen.getByTestId('oidc-test-connection-run-default') as HTMLButtonElement;
+    expect(btn.disabled).toBe(true);
+  });
+
+  it('HappyPath — renders all four primary checks green when discovery succeeds', async () => {
+    vi.mocked(client.authOIDCTestProvider).mockResolvedValue({
+      discovery_succeeded: true,
+      jwks_reachable: true,
+      supported_alg_values: ['RS256', 'ES256'],
+      iss_param_supported: true,
+      issuer_echo: 'https://idp.example.com',
+      authorization_url: 'https://idp.example.com/authorize',
+      token_url: 'https://idp.example.com/token',
+      jwks_uri: 'https://idp.example.com/jwks',
+      userinfo_endpoint: 'https://idp.example.com/userinfo',
+      errors: [],
+    });
+
+    render(
+      <OIDCTestConnectionPanel
+        issuerURL="https://idp.example.com"
+        clientID="certctl"
+        scopes={['openid', 'profile', 'email']}
+      />,
+    );
+
+    fireEvent.click(screen.getByTestId('oidc-test-connection-run-default'));
+    await waitFor(() => screen.getByTestId('oidc-test-connection-result-default'));
+
+    // All four primary checks visible + green.
+    expect(screen.getByTestId('oidc-test-connection-check-discovery-default').textContent)
+      .toContain('✓');
+    expect(screen.getByTestId('oidc-test-connection-check-jwks-default').textContent)
+      .toContain('✓');
+    expect(screen.getByTestId('oidc-test-connection-check-algs-default').textContent)
+      .toContain('✓');
+    // iss_param SUPPORTED → ✓, not `·`.
+    expect(screen.getByTestId('oidc-test-connection-check-iss-param-default').textContent)
+      .toContain('✓');
+
+    // Detail rows present.
+    expect(screen.getByTestId('oidc-test-connection-detail-authz-url-default')).toBeTruthy();
+    expect(screen.getByTestId('oidc-test-connection-detail-token-url-default')).toBeTruthy();
+    expect(screen.getByTestId('oidc-test-connection-detail-userinfo-url-default')).toBeTruthy();
+
+    // No errors block on happy path.
+    expect(screen.queryByTestId('oidc-test-connection-errors-list-default')).toBeNull();
+
+    // The mocked POST received the staged input.
+    expect(client.authOIDCTestProvider).toHaveBeenCalledTimes(1);
+    expect(client.authOIDCTestProvider).toHaveBeenCalledWith({
+      issuer_url: 'https://idp.example.com',
+      client_id: 'certctl',
+      scopes: ['openid', 'profile', 'email'],
+    });
+  });
+
+  it('FailurePath — renders the errors list when discovery_succeeded is false', async () => {
+    vi.mocked(client.authOIDCTestProvider).mockResolvedValue({
+      discovery_succeeded: false,
+      jwks_reachable: false,
+      supported_alg_values: [],
+      iss_param_supported: false,
+      errors: ['discovery fetch failed: connection refused', 'jwks_uri not advertised'],
+    });
+
+    render(
+      <OIDCTestConnectionPanel
+        issuerURL="https://broken.idp.example.com"
+        clientID="cid"
+        scopes={['openid']}
+      />,
+    );
+
+    fireEvent.click(screen.getByTestId('oidc-test-connection-run-default'));
+    await waitFor(() => screen.getByTestId('oidc-test-connection-result-default'));
+
+    // Discovery + JWKS marked ✗.
+    expect(screen.getByTestId('oidc-test-connection-check-discovery-default').textContent)
+      .toContain('✗');
+    expect(screen.getByTestId('oidc-test-connection-check-jwks-default').textContent)
+      .toContain('✗');
+    // Empty alg list → ⚠ warning, not ✗ (the IdP responded but advertised nothing).
+    expect(screen.getByTestId('oidc-test-connection-check-algs-default').textContent)
+      .toContain('⚠');
+
+    // Errors list rendered with both entries.
+    const errs = screen.getByTestId('oidc-test-connection-errors-list-default');
+    expect(errs.textContent).toContain('connection refused');
+    expect(errs.textContent).toContain('jwks_uri not advertised');
+  });
+
+  it('IssParamFalse — renders the informational `·` glyph when iss_param_supported is false', async () => {
+    vi.mocked(client.authOIDCTestProvider).mockResolvedValue({
+      discovery_succeeded: true,
+      jwks_reachable: true,
+      supported_alg_values: ['RS256'],
+      iss_param_supported: false,
+      issuer_echo: 'https://idp.example.com',
+      jwks_uri: 'https://idp.example.com/jwks',
+      errors: [],
+    });
+
+    render(
+      <OIDCTestConnectionPanel
+        issuerURL="https://idp.example.com"
+        clientID="cid"
+        scopes={['openid']}
+      />,
+    );
+
+    fireEvent.click(screen.getByTestId('oidc-test-connection-run-default'));
+    await waitFor(() => screen.getByTestId('oidc-test-connection-result-default'));
+
+    const issRow = screen.getByTestId('oidc-test-connection-check-iss-param-default');
+    expect(issRow.textContent).toContain('·');
+    // Must NOT be ✗ — RFC 9207 is SHOULD, not MUST; the panel must
+    // not visually mark this as a failure.
+    expect(issRow.textContent).not.toContain('✗');
+    // Body should explain that this is informational.
+    expect(issRow.textContent).toContain('informational');
+  });
+
+  it('FetchError — renders a top-level error when authOIDCTestProvider throws', async () => {
+    vi.mocked(client.authOIDCTestProvider).mockRejectedValue(new Error('network down'));
+
+    render(
+      <OIDCTestConnectionPanel
+        issuerURL="https://idp.example.com"
+        clientID="cid"
+        scopes={['openid']}
+      />,
+    );
+
+    fireEvent.click(screen.getByTestId('oidc-test-connection-run-default'));
+    await waitFor(() => screen.getByTestId('oidc-test-connection-error-default'));
+
+    expect(screen.getByTestId('oidc-test-connection-error-default').textContent)
+      .toContain('network down');
+    // The success result panel must NOT render alongside an error.
+    expect(screen.queryByTestId('oidc-test-connection-result-default')).toBeNull();
+  });
+
+  it('TestIDSuffix — same component renders twice on a page without colliding test IDs', async () => {
+    vi.mocked(client.authOIDCTestProvider).mockResolvedValue({
+      discovery_succeeded: true,
+      jwks_reachable: true,
+      supported_alg_values: ['RS256'],
+      iss_param_supported: false,
+    });
+
+    render(
+      <>
+        <OIDCTestConnectionPanel
+          issuerURL="https://idp.a.example.com"
+          clientID="a"
+          scopes={['openid']}
+          testIDSuffix="create"
+        />
+        <OIDCTestConnectionPanel
+          issuerURL="https://idp.b.example.com"
+          clientID="b"
+          scopes={['openid']}
+          testIDSuffix="edit"
+        />
+      </>,
+    );
+
+    // Both panels visible with distinct test IDs — no DOM-id collisions.
+    expect(screen.getByTestId('oidc-test-connection-panel-create')).toBeTruthy();
+    expect(screen.getByTestId('oidc-test-connection-panel-edit')).toBeTruthy();
+    expect(screen.getByTestId('oidc-test-connection-run-create')).toBeTruthy();
+    expect(screen.getByTestId('oidc-test-connection-run-edit')).toBeTruthy();
+  });
+});
diff --git a/web/src/pages/auth/OIDCTestConnectionPanel.tsx b/web/src/pages/auth/OIDCTestConnectionPanel.tsx
new file mode 100644
index 0000000..632180e
--- /dev/null
+++ b/web/src/pages/auth/OIDCTestConnectionPanel.tsx
@@ -0,0 +1,170 @@
+import { useState } from 'react';
+import { authOIDCTestProvider, type TestDiscoveryResult } from '../../api/client';
+
+// =============================================================================
+// Audit 2026-05-11 Fix 09 — Test Connection panel (MED-5 GUI half).
+//
+// MED-5 backend (`POST /api/v1/auth/oidc/test`, commit 00bbef7) shipped
+// the dry-run discovery + JWKS-reachability + alg-downgrade-defense probe
+// behind `authOIDCTestProvider` in the API client, but no caller existed
+// in the UI. Operators had to complete the create form blind, save, then
+// click "Refresh" to discover whether the issuer URL worked; failures
+// left a broken provider row in the DB that had to be deleted before
+// retrying. This panel surfaces the dry-run result before commit.
+//
+// Embedded above the Submit button on both the OIDCProvidersPage create
+// modal and the OIDCProviderDetailPage edit form. The component does
+// NOT persist anything — it's a pure read-only probe against the
+// configured issuer URL + client ID + scopes. Errors render inline; the
+// operator decides whether to proceed with the save.
+//
+// Why each line matters:
+//   - discovery_succeeded — did the well-known JSON fetch + parse?
+//   - jwks_reachable — does the advertised jwks_uri respond?
+//   - supported_alg_values — early warning if the IdP advertises only
+//     HS-family algs (RFC 7515 §A.2 / §A.3); the backend rejects these
+//     at create-time too, but seeing it here saves a round-trip.
+//   - iss_param_supported — RFC 9207 advertisement check. Informational
+//     only (the spec is a SHOULD, not a MUST); rendered as `·`, not ✗.
+//   - userinfo_endpoint — useful to see when fetch_userinfo is
+//     configured; absence means the IdP doesn't expose the endpoint at
+//     all (some custom OIDC servers omit it).
+//   - errors — backend-collected detail; one line per error.
+// =============================================================================
+
+interface Props {
+  issuerURL: string;
+  clientID: string;
+  /** Optional. Backend defaults to ['openid'] when empty; the panel
+   * passes whatever the caller has staged so a test against an IdP
+   * with custom scope requirements (e.g. Azure AD's `.default`) can
+   * verify reachability with the real scope set. */
+  scopes: string[];
+  /** Optional caller-supplied data-testid suffix so the same panel
+   * can render twice on the same page (e.g. create vs edit) without
+   * colliding test IDs. Defaults to `default`. */
+  testIDSuffix?: string;
+}
+
+export default function OIDCTestConnectionPanel({
+  issuerURL,
+  clientID,
+  scopes,
+  testIDSuffix = 'default',
+}: Props) {
+  const [busy, setBusy] = useState(false);
+  const [result, setResult] = useState<TestDiscoveryResult | null>(null);
+  const [err, setErr] = useState<string | null>(null);
+
+  const trimmedIssuer = issuerURL.trim();
+
+  async function run() {
+    if (!trimmedIssuer) {
+      // Defensive — the button is disabled when issuerURL is empty,
+      // but a programmatic click still goes through the same gate.
+      setErr('Issuer URL is required before testing.');
+      return;
+    }
+    setBusy(true);
+    setErr(null);
+    setResult(null);
+    try {
+      const r = await authOIDCTestProvider({
+        issuer_url: trimmedIssuer,
+        client_id: clientID,
+        scopes,
+      });
+      setResult(r);
+    } catch (e) {
+      setErr(e instanceof Error ? e.message : String(e));
+    } finally {
+      setBusy(false);
+    }
+  }
+
+  const tid = (s: string) => `oidc-test-connection-${s}-${testIDSuffix}`;
+
+  return (
+    <div
+      className="border border-surface-border rounded p-3 my-3"
+      data-testid={tid('panel')}
+    >
+      <div className="flex items-start justify-between gap-3">
+        <div className="flex-1">
+          <div className="font-semibold text-sm text-ink">Test connection</div>
+          <div className="text-xs text-ink-muted">
+            Dry-run OIDC discovery + JWKS reachability + alg-downgrade defense.
+            Does NOT persist; safe to run repeatedly before saving.
+          </div>
+        </div>
+        <button
+          type="button"
+          onClick={run}
+          disabled={busy || !trimmedIssuer}
+          className="px-3 py-1.5 text-sm border border-surface-border rounded bg-page hover:bg-surface text-ink disabled:opacity-50 whitespace-nowrap"
+          data-testid={tid('run')}
+        >
+          {busy ? 'Running…' : 'Run test'}
+        </button>
+      </div>
+      {err && (
+        <div
+          className="mt-2 text-xs text-red-700"
+          data-testid={tid('error')}
+        >
+          {err}
+        </div>
+      )}
+      {result && (
+        <ul
+          className="mt-3 text-xs space-y-1 text-ink"
+          data-testid={tid('result')}
+        >
+          <li data-testid={tid('check-discovery')}>
+            {result.discovery_succeeded ? '✓' : '✗'} Discovery fetched
+            {result.issuer_echo ? ` (issuer echoes: ${result.issuer_echo})` : ''}
+          </li>
+          <li data-testid={tid('check-jwks')}>
+            {result.jwks_reachable ? '✓' : '✗'} JWKS reachable
+            {result.jwks_uri ? ` (${result.jwks_uri})` : ' (no jwks_uri advertised)'}
+          </li>
+          <li data-testid={tid('check-algs')}>
+            {(result.supported_alg_values?.length ?? 0) > 0 ? '✓' : '⚠'} Supported algs:{' '}
+            <code className="font-mono">
+              {(result.supported_alg_values ?? []).join(', ') || '(none advertised)'}
+            </code>
+          </li>
+          <li data-testid={tid('check-iss-param')}>
+            {result.iss_param_supported ? '✓' : '·'} RFC 9207 iss parameter advertised:{' '}
+            {result.iss_param_supported ? 'yes' : 'no (informational — spec is SHOULD)'}
+          </li>
+          {result.authorization_url && (
+            <li className="text-ink-muted" data-testid={tid('detail-authz-url')}>
+              · Authorization URL: <code className="font-mono">{result.authorization_url}</code>
+            </li>
+          )}
+          {result.token_url && (
+            <li className="text-ink-muted" data-testid={tid('detail-token-url')}>
+              · Token URL: <code className="font-mono">{result.token_url}</code>
+            </li>
+          )}
+          {result.userinfo_endpoint && (
+            <li className="text-ink-muted" data-testid={tid('detail-userinfo-url')}>
+              · UserInfo endpoint: <code className="font-mono">{result.userinfo_endpoint}</code>
+            </li>
+          )}
+          {(result.errors ?? []).length > 0 && (
+            <li className="text-red-700 mt-2" data-testid={tid('errors-list')}>
+              <strong>Errors ({result.errors!.length}):</strong>
+              <ul className="ml-4 list-disc">
+                {result.errors!.map((e, i) => (
+                  <li key={i}>{e}</li>
+                ))}
+              </ul>
+            </li>
+          )}
+        </ul>
+      )}
+    </div>
+  );
+}