web: abstract rootInterface()?.config?.capabilities.includes() into .can() (#7737)

* This commit abstracts access to the object `rootInterface()?.config?` into a single accessor,
`authentikConfig`, that can be mixed into any AKElement object that requires access to it.

Since access to `rootInterface()?.config?` is _universally_ used for a single (and repetitive)
boolean check, a separate accessor has been provided that converts all calls of the form:

``` javascript
rootInterface()?.config?.capabilities.includes(CapabilitiesEnum.CanImpersonate)
```

into:

``` javascript
this.can(CapabilitiesEnum.CanImpersonate)
```

It does this via a Mixin, `WithCapabilitiesConfig`, which understands that these calls only make
sense in the context of a running, fully configured authentik instance, and that their purpose is to
inform authentik components of a user’s capabilities. The latter is why I don’t feel uncomfortable
turning a function call into a method; we should make it explicit that this is a relationship
between components.

The mixin has a single single field, `[WCC.capabilitiesConfig]`, where its association with the
upper-level configuration is made. If that syntax looks peculiar to you, good! I’ve used an explict
unique symbol as the field name; it is inaccessable an innumerable in the object list. The debugger
shows it only as:

    Symbol(): {
        cacheTimeout: 300
        cacheTimeoutFlows: 300
        cacheTimeoutPolicies: 300
        cacheTimeoutReputation: 300
        capabilities: (5) ['can_save_media', 'can_geo_ip', 'can_impersonate', 'can_debug', 'is_enterprise']
    }

Since you can’t reference it by identity, you can’t write to it. Until every browser supports actual
private fields, this is the best we can do; it does guarantee that field name collisions are
impossible, which is a win.

The mixin takes a second optional boolean; setting this to true will cause any web component using
the mixin to automatically schedule a re-render if the capabilities list changes.

The mixin is also generic; despite the "...into a Lit-Context" in the title, the internals of the
Mixin can be replaced with anything so long as the signature of `.can()` is preserved.

Because this work builds off the work I did to give the Sidebar access to the configuration without
ad-hoc retrieval or prop-drilling, it wasn’t necessary to create a new context for it. That will be
necessary for the following:

TODO:

``` javascript
rootInterface()?.uiConfig;
rootInterface()?.tenant;
me();
```

* web: Added a README with a description of the applications' "mental model," essentially an architectural description.

* web: prettier had opinions about the README

* web: Jens requested that subscription be  by default, and it's the right call.

* This commit abstracts access to the object `rootInterface()?.config?` into a single accessor,
`authentikConfig`, that can be mixed into any AKElement object that requires access to it.

Since access to `rootInterface()?.config?` is _universally_ used for a single (and repetitive)
boolean check, a separate accessor has been provided that converts all calls of the form:

``` javascript
rootInterface()?.config?.capabilities.includes(CapabilitiesEnum.CanImpersonate)
```

into:

``` javascript
this.can(CapabilitiesEnum.CanImpersonate)
```

It does this via a Mixin, `WithCapabilitiesConfig`, which understands that these calls only make
sense in the context of a running, fully configured authentik instance, and that their purpose is to
inform authentik components of a user’s capabilities. The latter is why I don’t feel uncomfortable
turning a function call into a method; we should make it explicit that this is a relationship
between components.

The mixin has a single single field, `[WCC.capabilitiesConfig]`, where its association with the
upper-level configuration is made. If that syntax looks peculiar to you, good! I’ve used an explict
unique symbol as the field name; it is inaccessable an innumerable in the object list. The debugger
shows it only as:

    Symbol(): {
        cacheTimeout: 300
        cacheTimeoutFlows: 300
        cacheTimeoutPolicies: 300
        cacheTimeoutReputation: 300
        capabilities: (5) ['can_save_media', 'can_geo_ip', 'can_impersonate', 'can_debug', 'is_enterprise']
    }

Since you can’t reference it by identity, you can’t write to it. Until every browser supports actual
private fields, this is the best we can do; it does guarantee that field name collisions are
impossible, which is a win.

The mixin takes a second optional boolean; setting this to true will cause any web component using
the mixin to automatically schedule a re-render if the capabilities list changes.

The mixin is also generic; despite the "...into a Lit-Context" in the title, the internals of the
Mixin can be replaced with anything so long as the signature of `.can()` is preserved.

Because this work builds off the work I did to give the Sidebar access to the configuration without
ad-hoc retrieval or prop-drilling, it wasn’t necessary to create a new context for it. That will be
necessary for the following:

TODO:

``` javascript
rootInterface()?.uiConfig;
rootInterface()?.tenant;
me();
```

* web: Added a README with a description of the applications' "mental model," essentially an architectural description.

* web: prettier had opinions about the README

* web: Jens requested that subscription be  by default, and it's the right call.

* web: adjust RAC to point to the (now independent) Interface.

- Also, removed redundant check.

web/src/elements/Interface/Interface.ts

@@ -0,0 +1,67 @@
+import { config, tenant } from "@goauthentik/common/api/config";
+import { UIConfig, uiConfig } from "@goauthentik/common/ui/config";
+import { authentikConfigContext } from "@goauthentik/elements/AuthentikContexts";
+import type { AdoptedStyleSheetsElement } from "@goauthentik/elements/types";
+import { ensureCSSStyleSheet } from "@goauthentik/elements/utils/ensureCSSStyleSheet";
+
+import { ContextProvider } from "@lit-labs/context";
+import { state } from "lit/decorators.js";
+
+import PFBase from "@patternfly/patternfly/patternfly-base.css";
+
+import { Config, CurrentTenant, UiThemeEnum } from "@goauthentik/api";
+
+import { AKElement } from "../Base";
+
+type AkInterface = HTMLElement & {
+    getTheme: () => Promise<UiThemeEnum>;
+    tenant?: CurrentTenant;
+    uiConfig?: UIConfig;
+    config?: Config;
+};
+
+export class Interface extends AKElement implements AkInterface {
+    @state()
+    tenant?: CurrentTenant;
+
+    @state()
+    uiConfig?: UIConfig;
+
+    _configContext = new ContextProvider(this, {
+        context: authentikConfigContext,
+        initialValue: undefined,
+    });
+
+    _config?: Config;
+
+    @state()
+    set config(c: Config) {
+        this._config = c;
+        this._configContext.setValue(c);
+        this.requestUpdate();
+    }
+
+    get config(): Config | undefined {
+        return this._config;
+    }
+
+    constructor() {
+        super();
+        document.adoptedStyleSheets = [...document.adoptedStyleSheets, ensureCSSStyleSheet(PFBase)];
+        tenant().then((tenant) => (this.tenant = tenant));
+        config().then((config) => (this.config = config));
+        this.dataset.akInterfaceRoot = "true";
+    }
+
+    _activateTheme(root: AdoptedStyleSheetsElement, theme: UiThemeEnum): void {
+        super._activateTheme(root, theme);
+        super._activateTheme(document, theme);
+    }
+
+    async getTheme(): Promise<UiThemeEnum> {
+        if (!this.uiConfig) {
+            this.uiConfig = await uiConfig();
+        }
+        return this.uiConfig.theme?.base || UiThemeEnum.Automatic;
+    }
+}

web/src/elements/Interface/authentikConfigProvider.ts

@@ -0,0 +1,20 @@
+import { authentikConfigContext } from "@goauthentik/elements/AuthentikContexts";
+
+import { consume } from "@lit-labs/context";
+import type { LitElement } from "lit";
+
+import type { Config } from "@goauthentik/api";
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+type Constructor<T = object> = new (...args: any[]) => T;
+
+export function WithAuthentikConfig<T extends Constructor<LitElement>>(
+    superclass: T,
+    subscribe = true,
+) {
+    class WithAkConfigProvider extends superclass {
+        @consume({ context: authentikConfigContext, subscribe })
+        public authentikConfig!: Config;
+    }
+    return WithAkConfigProvider;
+}

web/src/elements/Interface/capabilitiesProvider.ts

@@ -0,0 +1,69 @@
+import { authentikConfigContext } from "@goauthentik/elements/AuthentikContexts";
+
+import { consume } from "@lit-labs/context";
+import type { LitElement } from "lit";
+
+import { CapabilitiesEnum } from "@goauthentik/api";
+import { Config } from "@goauthentik/api";
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+type Constructor<T = object> = abstract new (...args: any[]) => T;
+
+// Using a unique, lexically scoped, and locally static symbol as the field name for the context
+// means that it's inaccessible to any child class looking for it. It's one of the strongest privacy
+// guarantees in JavaScript.
+
+class WCC {
+    public static readonly capabilitiesConfig: unique symbol = Symbol();
+}
+
+/**
+ * withCapabilitiesContext mixes in a single method to any LitElement, `can()`, which takes a
+ * CapabilitiesEnum and returns true or false.
+ *
+ * Usage:
+ *
+ * After importing, simply mixin this function:
+ *
+ * ```
+ * export class AkMyNiftyNewFeature extends withCapabilitiesContext(AKElement) {
+ * ```
+ *
+ * And then if you need to check on a capability:
+ *
+ * ```
+ * if (this.can(CapabilitiesEnum.IsEnterprise) { ... }
+ * ```
+ *
+ * This code re-exports CapabilitiesEnum, so you won't have to import it on a separate line if you
+ * don't need anything else from the API.
+ *
+ * Passing `true` as the second mixin argument will cause the inheriting class to subscribe to the
+ * configuration context. Should the context be explicitly reset, all active web components that are
+ * currently active and subscribed to the context will automatically have a `requestUpdate()`
+ * triggered with the new configuration.
+ *
+ */
+
+export function WithCapabilitiesConfig<T extends Constructor<LitElement>>(
+    superclass: T,
+    subscribe = true,
+) {
+    abstract class CapabilitiesContext extends superclass {
+        @consume({ context: authentikConfigContext, subscribe })
+        private [WCC.capabilitiesConfig]!: Config;
+
+        can(c: CapabilitiesEnum) {
+            if (!this[WCC.capabilitiesConfig]) {
+                throw new Error(
+                    "ConfigContext: Attempted to access site configuration before initialization.",
+                );
+            }
+            return this[WCC.capabilitiesConfig].capabilities.includes(c);
+        }
+    }
+
+    return CapabilitiesContext;
+}
+
+export { CapabilitiesEnum };

web/src/elements/Interface/index.ts

@@ -0,0 +1,4 @@
+import { Interface } from "./Interface";
+
+export { Interface };
+export default Interface;