feat(provider): Add United Effects provider (#4546)

* Adding United Effects as a provider
* Update packages/next-auth/src/providers/united-effects.ts
* returning name and image as null in profile response

Co-authored-by: Lluis Agusti <hi@llu.lu>

docs/docs/providers/united-effects.md

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+---
+id: united-effects
+title: United Effects
+---
+
+## Documentation
+
+https://docs.unitedeffects.com/integrations/nextauthjs
+
+## Configuration
+
+https://core.unitedeffects.com
+
+## Options
+
+The **United Effects Provider** comes with a set of default options:
+
+- [United Effects Provider options](https://github.com/nextauthjs/next-auth/blob/main/packages/next-auth/src/providers/united-effects.ts)
+
+You can override any of the options to suit your own use case.
+
+## Example
+
+```js
+import UnitedEffectsProvider from "next-auth/providers/united-effects";
+...
+providers: [
+  UnitedEffectsProvider({
+    clientId: process.env.UNITED_EFFECTS_CLIENT_ID,
+    clientSecret: process.env.UNITED_EFFECTS_CLIENT_SECRET,
+    issuer: process.env.UNITED_EFFECTS_ISSUER
+  })
+]
+...
+```
+
+:::note
+`issuer` should be the fully qualified URL including your Auth Group ID – e.g. `https://auth.unitedeffects.com/YQpbQV5dbW-224dCovz-3`
+:::
+
+:::warning
+The United Effects API does not return the user name or image by design, so this provider will return null for both. United Effects prioritizes user personal information security above all and has built a secured profile access request system separate from the provider API.
+:::

packages/next-auth/src/providers/united-effects.ts

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+import type { OAuthConfig, OAuthUserConfig } from "."
+
+export interface UnitedEffectsProfile extends Record<string, any> {
+  sub: string
+  email: string
+}
+
+export default function UnitedEffects<P extends UnitedEffectsProfile>(
+  options: OAuthUserConfig<P> & { issuer: string }
+): OAuthConfig<P> {
+  return {
+    id: "united-effects",
+    name: "United Effects",
+    wellKnown: `${options.issuer}/.well-known/openid-configuration`,
+    type: "oauth",
+    authorization: {
+      params: { scope: "openid email profile", resource: options.issuer },
+    },
+    checks: ["pkce", "state"],
+    idToken: true,
+    profile(profile) {
+      return {
+        id: profile.sub,
+        name: null,
+        email: profile.email,
+        image: null,
+      }
+    },
+    options,
+  }
+}