You can configure your SharePoint Framework components to be immediately available across the tenant when the solution package is installed to the tenant app catalog. This can be configured by using the skipFeatureDeployment attribute in the package-solution.json file.

Reference:
https://docs.microsoft.com/en-us/microsoftteams/platform/concepts/build-and-test/deep-links

In web server apps, the sign-in authentication flow takes these high-level steps:

You can ensure the user's identity by validating the ID token with a public signing key that is received from the Microsoft identity platform endpoint. A session cookie is set, which can be used to identify the user on subsequent page requests.
In addition to simple sign-in, a web server app might need to access another web service, such as a REST API. In this case, the web server app engages in a combined OpenID Connect and OAuth 2.0 flow, by using the OAuth 2.0 authorization code flow.

MSGraphClient is a new HTTP client introduced in SharePoint Framework v1.6.0 that simplifies connecting to the Microsoft Graph inside SharePoint Framework solutions.
With MS Graph we use MSGraphClient to get information about the current user; this.context.msGraphClientFactory
.getClient()
.then((client: MSGraphClient): void => {
// get information about the current user from the Microsoft Graph
client
.api('/me')
.get((error, response: any, rawResponse?: any) => {
// handle the response
});
});
Reference:
https://www.c-sharpcorner.com/article/show-outlook-messages-from-microsoft-graph-in-spfx-client-side-web-part/