Allow creating Grafana API keys from Cloud (#69)

* Allow creating Grafana API keys from Cloud
Also add a function to create a temporary client. This will be used by Terraform. See grafana/terraform-provider-grafana#416

* Apply suggestions from code review

Co-authored-by: Leandro López <leandro.lopez@grafana.com>

Co-authored-by: Leandro López <leandro.lopez@grafana.com>

cloud_grafana_api_key.go

@@ -0,0 +1,57 @@
+package gapi
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+// This function creates a API key inside the Grafana instance running in stack `stack`. It's used in order
+// to provision API keys inside Grafana while just having access to a Grafana Cloud API key.
+//
+// See https://grafana.com/docs/grafana-cloud/api/#create-grafana-api-keys for more information.
+func (c *Client) CreateGrafanaAPIKeyFromCloud(stack string, input *CreateAPIKeyRequest) (*CreateAPIKeyResponse, error) {
+	data, err := json.Marshal(input)
+	if err != nil {
+		return nil, err
+	}
+
+	resp := &CreateAPIKeyResponse{}
+	err = c.request("POST", fmt.Sprintf("/api/instances/%s/api/auth/keys", stack), nil, bytes.NewBuffer(data), resp)
+	return resp, err
+}
+
+// The Grafana Cloud API is disconnected from the Grafana API on the stacks unfortunately. That's why we can't use
+// the Grafana Cloud API key to fully manage API keys on the Grafana API. The only thing we can do is to create
+// a temporary Admin key, and create a Grafana API client with that.
+func (c *Client) CreateTemporaryStackGrafanaClient(stackSlug, tempKeyPrefix string, tempKeyDuration time.Duration) (tempClient *Client, cleanup func() error, err error) {
+	stack, err := c.StackBySlug(stackSlug)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	name := fmt.Sprintf("%s-%d", tempKeyPrefix, time.Now().UnixNano())
+	req := &CreateAPIKeyRequest{
+		Name:          name,
+		Role:          "Admin",
+		SecondsToLive: int64(tempKeyDuration.Seconds()),
+	}
+
+	apiKey, err := c.CreateGrafanaAPIKeyFromCloud(stackSlug, req)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	client, err := New(stack.URL, Config{APIKey: apiKey.Key})
+	if err != nil {
+		return nil, nil, err
+	}
+
+	cleanup = func() error {
+		_, err = client.DeleteAPIKey(apiKey.ID)
+		return err
+	}
+
+	return client, cleanup, nil
+}