diff --git a/UAT_PLAYBOOK.md b/UAT_PLAYBOOK.md
index 5218977..166cf68 100644
--- a/UAT_PLAYBOOK.md
+++ b/UAT_PLAYBOOK.md
@@ -163,6 +163,10 @@ GroomBook API is a Hono-based REST service (TypeScript/Node.js) powering the pet
 | TC-API-8.5 | Add waitlist entry | POST /api/portal/waitlist with pet and service | 201 Created, waitlist entry created |
 | TC-API-8.6 | View portal invoices | GET /api/portal/invoices | 200 OK, list of client's invoices returned |
 | TC-API-8.7 | Pay multiple invoices | POST /api/portal/invoices/pay-multiple with invoice IDs | 200 OK, payment intent created |
+| TC-API-8.8 | SSO bridge — valid Better Auth session | POST /api/portal/session-from-auth with valid Better Auth session cookie (authenticated SSO user with matching client email) | 201 Created, `{sessionId, clientId, clientName}` returned |
+| TC-API-8.9 | SSO bridge — no Better Auth session | POST /api/portal/session-from-auth without Better Auth session cookie | 401 Unauthorized |
+| TC-API-8.10 | SSO bridge — no matching client | POST /api/portal/session-from-auth with valid Better Auth session for a user with no client record | 404 Not Found, error "No client record found for this user" |
+| TC-API-8.11 | SSO bridge — returned session works on portal routes | After TC-API-8.8, use returned sessionId as `X-Impersonation-Session-Id` header on GET /api/portal/me | 200 OK, client profile returned |
 
 ### 4.9 Waitlist
 
diff --git a/src/__tests__/portalSessionFromAuth.test.ts b/src/__tests__/portalSessionFromAuth.test.ts
new file mode 100644
index 0000000..8448803
--- /dev/null
+++ b/src/__tests__/portalSessionFromAuth.test.ts
@@ -0,0 +1,175 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { Hono } from "hono";
+import { getAuth } from "../lib/auth.js";
+
+const CLIENT_ID = "550e8400-e29b-41d4-a716-446655440001";
+const CLIENT_EMAIL = "alice@example.com";
+const CLIENT_NAME = "Alice Smith";
+
+const BETTER_AUTH_SESSION = {
+  user: {
+    id: "auth-user-001",
+    email: CLIENT_EMAIL,
+    name: CLIENT_NAME,
+  },
+  session: {
+    id: "ba-session-001",
+    expiresAt: new Date(Date.now() + 60 * 60 * 1000),
+  },
+};
+
+const MOCK_CLIENT = {
+  id: CLIENT_ID,
+  email: CLIENT_EMAIL,
+  name: CLIENT_NAME,
+};
+
+let mockGetAuth: ReturnType<typeof vi.fn>;
+let mockGetSession: ReturnType<typeof vi.fn>;
+let insertedSession: Record<string, unknown> | null = null;
+let mockClientRow: Record<string, unknown> | null = null;
+let mockStaffRow: Record<string, unknown> | null = null;
+
+function makeChainable(data: unknown[]): unknown {
+  const arr = [...data];
+  return new Proxy(arr, {
+    get(target, prop) {
+      if (prop === "where" || prop === "orderBy" || prop === "limit") {
+        return () => makeChainable(target);
+      }
+      // @ts-expect-error proxy
+      return target[prop];
+    },
+  });
+}
+
+vi.mock("@groombook/db", () => {
+  const impersonationSessions = new Proxy(
+    { _name: "impersonationSessions" },
+    { get: (t, p) => (p === "_name" ? "impersonationSessions" : { table: "impersonationSessions", column: p }) }
+  );
+
+  const clients = new Proxy(
+    { _name: "clients" },
+    { get: (t, p) => (p === "_name" ? "clients" : { table: "clients", column: p }) }
+  );
+
+  const staff = new Proxy(
+    { _name: "staff" },
+    { get: (t, p) => (p === "_name" ? "staff" : { table: "staff", column: p }) }
+  );
+
+  return {
+    getDb: () => ({
+      select: () => ({
+        from: (table: { _name: string }) => {
+          if (table._name === "clients") {
+            return makeChainable(mockClientRow ? [mockClientRow] : []);
+          }
+          if (table._name === "staff") {
+            return makeChainable(mockStaffRow ? [mockStaffRow] : []);
+          }
+          return makeChainable([]);
+        },
+      }),
+      insert: (table: { _name: string }) => ({
+        values: (vals: Record<string, unknown>) => ({
+          returning: () => {
+            if (table._name === "impersonationSessions") {
+              insertedSession = { id: "new-session-001", ...vals };
+              return [insertedSession];
+            }
+            return [];
+          },
+        }),
+      }),
+    }),
+    impersonationSessions,
+    clients,
+    staff,
+    eq: vi.fn(),
+    and: vi.fn(),
+    inArray: vi.fn(),
+  };
+});
+
+vi.mock("../lib/auth.js", () => ({
+  getAuth: vi.fn(),
+}));
+
+const { portalRouter } = await import("../routes/portal.js");
+
+const app = new Hono();
+app.route("/portal", portalRouter);
+
+describe("POST /portal/session-from-auth", () => {
+  beforeEach(() => {
+    insertedSession = null;
+    mockClientRow = null;
+    mockStaffRow = null;
+    mockGetSession = vi.fn();
+    mockGetAuth = vi.fn(() => ({
+      api: {
+        getSession: mockGetSession,
+      },
+    }));
+    vi.mocked(getAuth).mockImplementation(mockGetAuth);
+  });
+
+  it("returns 401 when no Better Auth session", async () => {
+    mockGetSession.mockResolvedValue(null);
+    const res = await app.request("/portal/session-from-auth", {
+      method: "POST",
+    });
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body.error).toBe("Unauthorized");
+  });
+
+  it("returns 404 when authenticated user has no client record", async () => {
+    mockGetSession.mockResolvedValue(BETTER_AUTH_SESSION);
+    mockClientRow = null;
+    const res = await app.request("/portal/session-from-auth", {
+      method: "POST",
+    });
+    expect(res.status).toBe(404);
+    const body = await res.json();
+    expect(body.error).toBe("No client record found for this user");
+  });
+
+  it("returns a portal session with sessionId, clientId, clientName when client is found", async () => {
+    mockGetSession.mockResolvedValue(BETTER_AUTH_SESSION);
+    mockClientRow = MOCK_CLIENT;
+    mockStaffRow = { id: "00000000-0000-0000-0000-000000000001" };
+    const res = await app.request("/portal/session-from-auth", {
+      method: "POST",
+    });
+    expect(res.status).toBe(201);
+    const body = await res.json();
+    expect(body).toHaveProperty("sessionId");
+    expect(body).toHaveProperty("clientId", CLIENT_ID);
+    expect(body).toHaveProperty("clientName", CLIENT_NAME);
+  });
+
+  it("creates a portal session with reason sso-bridge", async () => {
+    mockGetSession.mockResolvedValue(BETTER_AUTH_SESSION);
+    mockClientRow = MOCK_CLIENT;
+    mockStaffRow = { id: "00000000-0000-0000-0000-000000000001" };
+    const res = await app.request("/portal/session-from-auth", {
+      method: "POST",
+    });
+    expect(res.status).toBe(201);
+    expect(insertedSession).not.toBeNull();
+    expect((insertedSession as Record<string, unknown>).reason).toBe("sso-bridge");
+  });
+
+  it("returns 503 when auth is not configured", async () => {
+    mockGetAuth.mockImplementation(() => {
+      throw new Error("Auth not initialized");
+    });
+    const res = await app.request("/portal/session-from-auth", {
+      method: "POST",
+    });
+    expect(res.status).toBe(503);
+  });
+});
\ No newline at end of file
diff --git a/src/lib/auth.ts b/src/lib/auth.ts
index da2b2d1..ff1e125 100644
--- a/src/lib/auth.ts
+++ b/src/lib/auth.ts
@@ -172,7 +172,7 @@ export async function initAuth(): Promise<void> {
         clientSecret: oidcClientSecret,
         issuerUrl: oidcIssuer,
         internalBaseUrl: process.env.OIDC_INTERNAL_BASE,
-        scopes: "openid profile email",
+        scopes: "openid profile email role",
       };
       console.log("[auth] Using env var config (no DB config found)");
     }
diff --git a/src/routes/portal.ts b/src/routes/portal.ts
index a4c2b87..05b09ed 100644
--- a/src/routes/portal.ts
+++ b/src/routes/portal.ts
@@ -71,6 +71,78 @@ portalRouter.post(
   }
 );
 
+// Bridge Better Auth session → portal session for real SSO customers (GRO-1866).
+// Registered BEFORE the /* middleware so it is NOT subject to validatePortalSession.
+import { getAuth } from "../lib/auth.js";
+
+portalRouter.post("/session-from-auth", async (c) => {
+  let auth;
+  try {
+    auth = getAuth();
+  } catch {
+    return c.json({ error: "Authentication not configured" }, 503);
+  }
+
+  const session = await auth.api.getSession({
+    headers: c.req.raw.headers,
+  });
+
+  if (!session) {
+    return c.json({ error: "Unauthorized" }, 401);
+  }
+
+  const db = getDb();
+  const [client] = await db
+    .select()
+    .from(clients)
+    .where(eq(clients.email, session.user.email))
+    .limit(1);
+
+  if (!client) {
+    return c.json({ error: "No client record found for this user" }, 404);
+  }
+
+  const DEMO_STAFF_ID = "00000000-0000-0000-0000-000000000001";
+
+  let staffId = DEMO_STAFF_ID;
+  const [demoStaff] = await db
+    .select({ id: staff.id })
+    .from(staff)
+    .where(eq(staff.id, DEMO_STAFF_ID))
+    .limit(1);
+
+  if (!demoStaff) {
+    const [firstStaff] = await db
+      .select({ id: staff.id })
+      .from(staff)
+      .where(eq(staff.active, true))
+      .limit(1);
+    if (!firstStaff) {
+      return c.json({ error: "No staff records found" }, 500);
+    }
+    staffId = firstStaff.id;
+  }
+
+  const [portalSession] = await db
+    .insert(impersonationSessions)
+    .values({
+      staffId,
+      clientId: client.id,
+      reason: "sso-bridge",
+      expiresAt: new Date(Date.now() + 24 * 60 * 60 * 1000),
+    })
+    .returning();
+
+  return c.json(
+    {
+      sessionId: portalSession.id,
+      clientId: client.id,
+      clientName: client.name,
+    },
+    201
+  );
+});
+
 // Apply middleware to all portal routes
 portalRouter.use("/*", validatePortalSession, portalAudit);