revert(azure): revert removal (#3890)

* Revert "fix(sidebar): show docker sidebar when needed (#3852)"

This reverts commit 59da17dde4.

* Revert "refactor(azure): remove Azure ACI endpoint support (#3803)"

This reverts commit 493de20540.

api/http/proxy/factory/azure/transport.go

@@ -0,0 +1,80 @@
+package azure
+
+import (
+	"net/http"
+	"strconv"
+	"sync"
+	"time"
+
+	"github.com/portainer/portainer/api"
+	"github.com/portainer/portainer/api/http/client"
+)
+
+type (
+	azureAPIToken struct {
+		value          string
+		expirationTime time.Time
+	}
+
+	Transport struct {
+		credentials *portainer.AzureCredentials
+		client      *client.HTTPClient
+		token       *azureAPIToken
+		mutex       sync.Mutex
+	}
+)
+
+// NewTransport returns a pointer to a new instance of Transport that implements the HTTP Transport
+// interface for proxying requests to the Azure API.
+func NewTransport(credentials *portainer.AzureCredentials) *Transport {
+	return &Transport{
+		credentials: credentials,
+		client:      client.NewHTTPClient(),
+	}
+}
+
+// RoundTrip is the implementation of the the http.RoundTripper interface
+func (transport *Transport) RoundTrip(request *http.Request) (*http.Response, error) {
+	err := transport.retrieveAuthenticationToken()
+	if err != nil {
+		return nil, err
+	}
+
+	request.Header.Set("Authorization", "Bearer "+transport.token.value)
+	return http.DefaultTransport.RoundTrip(request)
+}
+
+func (transport *Transport) authenticate() error {
+	token, err := transport.client.ExecuteAzureAuthenticationRequest(transport.credentials)
+	if err != nil {
+		return err
+	}
+
+	expiresOn, err := strconv.ParseInt(token.ExpiresOn, 10, 64)
+	if err != nil {
+		return err
+	}
+
+	transport.token = &azureAPIToken{
+		value:          token.AccessToken,
+		expirationTime: time.Unix(expiresOn, 0),
+	}
+
+	return nil
+}
+
+func (transport *Transport) retrieveAuthenticationToken() error {
+	transport.mutex.Lock()
+	defer transport.mutex.Unlock()
+
+	if transport.token == nil {
+		return transport.authenticate()
+	}
+
+	timeLimit := time.Now().Add(-5 * time.Minute)
+	if timeLimit.After(transport.token.expirationTime) {
+		return transport.authenticate()
+	}
+
+	return nil
+}