feat: oidc-client.js based Svelte OidcComponent

follows a pattern similar to @dopry/svelte-auth0,
but uses the more standards compliant oidc-client.js
library.

README.md

@@ -0,0 +1,79 @@
+# svelte-oidc
+
+An Oidc Client Component for Svelte.
+
+[Try out the demo](https://darrelopry.com/svelte-oidc/)
+
+## Getting Started
+
+Setup an OIDC Sever
+ * https://www.ory.sh/
+ * https://www.keycloak.org/
+ * https://www.okta.com/
+ * http://auth0.com/
+
+ Get the authority and client_id
+
+`npm install @dopry/svelte-oidc`
+
+App.svelte
+```
+# App.svelte
+import {
+  OidcContext,
+  authError,
+  authToken,
+  idToken,
+  isAuthenticated,
+  isLoading,
+  login,
+  logout,
+  userInfo,
+} from '@dopry/svelte-oidc';
+</script>
+
+<OidcContext domain="dev-hvw40i79.auth0.com" client_id="aOijZt2ug6Ovgzp0HXdF23B6zxwA6PaP">
+  <button on:click|preventDefault='{() => login() }'>Login</button>
+  <button on:click|preventDefault='{() => logout() }'>Logout</button><br />
+  <pre>isLoading: {$isLoading}</pre>
+  <pre>isAuthenticated: {$isAuthenticated}</pre>
+  <pre>authToken: {$authToken}</pre>
+  <pre>idToken: {$authToken}</pre>
+  <pre>userInfo: {JSON.stringify($userInfo, null, 2)}</pre>
+  <pre>authError: {$authError}</pre>
+</OidcContext>
+```
+
+## Docs
+
+### Components
+* OidcContext - component to initiate the OIDC client. You only need one instance in your DOM tree at the root.
+
+  Attributes:
+  * authority - OIDC Authority/issuer/base url for .well-known/openid-configuration
+  * client_id - OAuth ClientId
+  * redirect_uri -  default: window.location.href
+  * post_logout_redirect_uri - override the default url that OIDC will redirect to after logout. default: window.location.href
+
+### Functions
+* login(preseveRoute = true, callback_url = null) - begin a user login.
+* logout(logout_url = null) - logout a user.
+* refreshToken - function to refresh a token.
+
+### Stores
+* isLoading - if true OIDC Context is still loading.
+* isAuthenticated - true if user is currently authenticated
+* authToken - api token
+* userInfo - the currently logged in user's info from OIDC
+* authError - the last authentication error.
+
+### Constants
+* OIDC_CONTEXT_CALLBACK_URL,
+* OIDC_CONTEXT_CLIENT_PROMISE - key for the OIDC client in setContext/getContext.
+* OIDC_CONTEXT_LOGOUT_URL,
+
+## Release
+**use semver**
+npm publish
+npm showcase:build
+npm showcase:publish