docs: add quickstart for go (#1635)

* docs: add quickstart for go

* some improvements

* change to md links

docs/docs/quickstarts/go.md

@@ -0,0 +1,142 @@
+---
+title: Go
+---
+
+This integration guide shows you how to integrate **ZITADEL** into your Go application.
+It demonstrates how to fetch some data from the ZITADEL management API.
+
+At the end of the guide you should have an application able read the details of your organisation.
+
+## Prerequisites
+
+The client [SDK](https://github.com/caos/zitadel-go) will handle all necessary OAuth 2.0 requests and send the required headers to the ZITADEL API using our [OIDC client library](https://github.com/caos/oidc).
+All that is required, is a service account with an Org Owner role assigned and its key JSON.
+
+However, we recommend you read the guide on [how to access ZITADEL API](../guides/access-zitadel-apis) and the associated guides for a basic knowledge of :
+ - [Recommended Authorization Flows](../guides/oauth-recommended-flows)
+ - [Service Users](../guides/serviceusers)
+
+> Be sure to have a valid key JSON and that its service account is either ORG_OWNER or at least ORG_OWNER_VIEWER before you continue with this guide.
+
+## Go Setup
+
+### Add Go SDK to your project
+
+You need to add the SDK into Go Modules by:
+
+```bash
+go get github.com/caos/zitadel-go
+```
+
+### Create example client
+
+Create a new go file with the content below. This will create a client for the management api and call its `GetMyOrg` function.
+The SDK will make sure you will have access to the API by retrieving a Bearer Token using JWT Profile with the provided scopes (`openid` and `urn:zitadel:iam:org:project:id:69234237810729019:aud`).
+
+```go
+package main
+
+import (
+    "context"
+    "log"
+    
+    "github.com/caos/oidc/pkg/oidc"
+    
+    "github.com/caos/zitadel-go/pkg/client/management"
+    "github.com/caos/zitadel-go/pkg/client/middleware"
+    "github.com/caos/zitadel-go/pkg/client/zitadel"
+    pb "github.com/caos/zitadel-go/pkg/client/zitadel/management"
+)
+
+
+func main() {
+    client, err := management.NewClient(
+        []string{oidc.ScopeOpenID, zitadel.ScopeZitadelAPI()},
+    )
+    if err != nil {
+        log.Fatalln("could not create client", err)
+    }
+    defer func() {
+        err := client.Connection.Close()
+        if err != nil {
+            log.Println("could not close grpc connection", err)
+        }
+    }()
+    
+    ctx := context.Background()
+    resp, err := client.GetMyOrg(ctx, &pb.GetMyOrgRequest{})
+    if err != nil {
+        log.Fatalln("call failed: ", err)
+    }
+    log.Printf("%s was created on: %s", resp.Org.Name, resp.Org.Details.CreationDate.AsTime())
+}
+```
+
+#### Key JSON
+
+To provide the key JSON to the SDK, simply set an environment variable `ZITADEL_KEY_PATH` with the path to the JSON as value.
+
+```bash
+export ZITADEL_KEY_PATH=/Users/test/servicekey.json
+```
+
+For development purposes you should be able to set this in your IDE.
+
+If you're not able to set it via environment variable, you can also pass it with an additional option:
+
+```go
+client, err := management.NewClient(
+    []string{oidc.ScopeOpenID, zitadel.ScopeZitadelAPI()},
+    zitadel.WithKeyPath("/Users/test/servicekey.json"),
+)
+```
+
+#### Custom ZITADEL instance
+
+If your client will not use ZITADEL Cloud (zitadel.ch), be sure to provide the correct values for the ZITADEL ProjectID, Issuer and API options:
+```go
+client, err := management.NewClient(
+    []string{oidc.ScopeOpenID, zitadel.ScopeProjectID("ZITADEL-ProjectID")},
+    zitadel.WithCustomURL("https://issuer.custom.ch", "api.custom.ch:443")
+)
+```
+
+### Test client
+
+After you have configured everything correctly, you can simply start the example by:
+
+```bash
+go run main.go
+```
+
+This will output something similar to:
+
+```
+2021/04/21 11:27:36 DemoOrg was created on: 2021-04-08 13:36:05.578194 +0000 UTC
+```
+
+## Completion
+
+You have successfully used the ZITADEL Go SDK to call the management API!
+
+If you encountered an error (e.g. `code = PermissionDenied desc = No matching permissions found`), 
+ensure your service user has the required permissions by assigning the `ORG_OWNER` or `ORG_OWNER_VIEWER` role
+and check the mentioned [guides](#prerequisites) at the beginning.
+
+If you've run into any other problem, don't hesitate to contact us or raise an issue on [ZITADEL](https://github.com/caos/zitadel/issues) or in the [SDK](https://github.com/caos/zitadel-go/issues).
+
+### Whats next?
+
+Now you can proceed implementing our APIs by adding more calls or trying to overwrite the organisation context:
+
+```go
+    respOverwrite, err := client.GetMyOrg(middleware.SetOrgID(ctx, "74161146763996133"), &pb.GetMyOrgRequest{})
+    if err != nil {
+        log.Fatalln("call failed: ", err)
+    }
+    log.Printf("%s was created on: %s", respOverwrite.Org.Name, respOverwrite.Org.Details.CreationDate.AsTime())
+}
+```
+Checkout more [examples from the SDK](https://github.com/caos/zitadel-go/blob/main/example) or refer to our [API Docs](../apis/introduction).
+
+> This guide will be updated soon to show you how to use the SDK for your own API as well.

docs/sidebars.js

@@ -22,6 +22,11 @@ module.exports = {
       items: ['quickstarts/angular'],
       collapsed: false,
     },
+    {
+      type: 'category',
+      label: 'Backends',
+      items: ['quickstarts/go'],
+    },
     {
       type: 'category',
       label: 'Identity Aware Proxy',