# Azure Active Directory authentication for Go

This is a standalone package for authenticating with Azure Active
Directory from other Go libraries and applications, in particular the [Azure SDK
for Go](https://github.com/Azure/azure-sdk-for-go).

Note: Despite the package's name it is not related to other "ADAL" libraries
maintained in the [github.com/AzureAD](https://github.com/AzureAD) org. Issues
should be opened in [this repo's](https://github.com/Azure/go-autorest/issues)
or [the SDK's](https://github.com/Azure/azure-sdk-for-go/issues) issue
trackers.

## Install

```bash
go get -u github.com/Azure/go-autorest/autorest/adal
```

## Usage

An Active Directory application is required in order to use this library. An application can be registered in the [Azure Portal](https://portal.azure.com/) by following these [guidelines](https://docs.microsoft.com/en-us/azure/active-directory/develop/active-directory-integrating-applications) or using the [Azure CLI](https://github.com/Azure/azure-cli).

### Register an Azure AD Application with secret


1. Register a new application with a `secret` credential

   ```
   az ad app create \
      --display-name example-app \
      --homepage https://example-app/home \
      --identifier-uris https://example-app/app \
      --password secret
   ```

2. Create a service principal using the `Application ID` from previous step

   ```
   az ad sp create --id "Application ID"
   ```

   * Replace `Application ID` with `appId` from step 1.

### Register an Azure AD Application with certificate

1. Create a private key

   ```
   openssl genrsa -out "example-app.key" 2048
   ```

2. Create the certificate

   ```
   openssl req -new -key "example-app.key" -subj "/CN=example-app" -out "example-app.csr"
   openssl x509 -req -in "example-app.csr" -signkey "example-app.key" -out "example-app.crt" -days 10000
   ```

3. Create the PKCS12 version of the certificate containing also the private key

   ```
   openssl pkcs12 -export -out "example-app.pfx" -inkey "example-app.key" -in "example-app.crt" -passout pass:

   ```

4. Register a new application with the certificate content form `example-app.crt`

   ```
   certificateContents="$(tail -n+2 "example-app.crt" | head -n-1)"

   az ad app create \
      --display-name example-app \
      --homepage https://example-app/home \
      --identifier-uris https://example-app/app \
      --key-usage Verify --end-date 2018-01-01 \
      --key-value "${certificateContents}"
   ```

5. Create a service principal using the `Application ID` from previous step

   ```
   az ad sp create --id "APPLICATION_ID"
   ```

   * Replace `APPLICATION_ID` with `appId` from step 4.


### Grant the necessary permissions

Azure relies on a Role-Based Access Control (RBAC) model to manage the access to resources at a fine-grained
level. There is a set of [pre-defined roles](https://docs.microsoft.com/en-us/azure/active-directory/role-based-access-built-in-roles)
which can be assigned to a service principal of an Azure AD application depending of your needs.

```
az role assignment create --assigner "SERVICE_PRINCIPAL_ID" --role "ROLE_NAME"
```

* Replace the `SERVICE_PRINCIPAL_ID` with the `appId` from previous step.
* Replace the `ROLE_NAME` with a role name of your choice.

It is also possible to define custom role definitions.

```
az role definition create --role-definition role-definition.json
```

* Check [custom roles](https://docs.microsoft.com/en-us/azure/active-directory/role-based-access-control-custom-roles) for more details regarding the content of `role-definition.json` file.


### Acquire Access Token

The common configuration used by all flows:

```Go
const activeDirectoryEndpoint = "https://login.microsoftonline.com/"
tenantID := "TENANT_ID"
oauthConfig, err := adal.NewOAuthConfig(activeDirectoryEndpoint, tenantID)

applicationID := "APPLICATION_ID"

callback := func(token adal.Token) error {
    // This is called after the token is acquired
}

// The resource for which the token is acquired
resource := "https://management.core.windows.net/"
```

* Replace the `TENANT_ID` with your tenant ID.
* Replace the `APPLICATION_ID` with the value from previous section.

#### Client Credentials

```Go
applicationSecret := "APPLICATION_SECRET"

spt, err := adal.NewServicePrincipalToken(
	oauthConfig,
	appliationID,
	applicationSecret,
	resource,
	callbacks...)
if err != nil {
	return nil, err
}

// Acquire a new access token
err  = spt.Refresh()
if (err == nil) {
    token := spt.Token
}
```

* Replace the `APPLICATION_SECRET` with the `password` value from previous section.

#### Client Certificate

```Go
certificatePath := "./example-app.pfx"

certData, err := ioutil.ReadFile(certificatePath)
if err != nil {
	return nil, fmt.Errorf("failed to read the certificate file (%s): %v", certificatePath, err)
}

// Get the certificate and private key from pfx file
certificate, rsaPrivateKey, err := decodePkcs12(certData, "")
if err != nil {
	return nil, fmt.Errorf("failed to decode pkcs12 certificate while creating spt: %v", err)
}

spt, err := adal.NewServicePrincipalTokenFromCertificate(
	oauthConfig,
	applicationID,
	certificate,
	rsaPrivateKey,
	resource,
	callbacks...)

// Acquire a new access token
err  = spt.Refresh()
if (err == nil) {
    token := spt.Token
}
```

* Update the certificate path to point to the example-app.pfx file which was created in previous section.


#### Device Code

```Go
oauthClient := &http.Client{}

// Acquire the device code
deviceCode, err := adal.InitiateDeviceAuth(
	oauthClient,
	oauthConfig,
	applicationID,
	resource)
if err != nil {
	return nil, fmt.Errorf("Failed to start device auth flow: %s", err)
}

// Display the authentication message
fmt.Println(*deviceCode.Message)

// Wait here until the user is authenticated
token, err := adal.WaitForUserCompletion(oauthClient, deviceCode)
if err != nil {
	return nil, fmt.Errorf("Failed to finish device auth flow: %s", err)
}

spt, err := adal.NewServicePrincipalTokenFromManualToken(
	oauthConfig,
	applicationID,
	resource,
	*token,
	callbacks...)

if (err == nil) {
    token := spt.Token
}
```

#### Username password authenticate

```Go
spt, err := adal.NewServicePrincipalTokenFromUsernamePassword(
	oauthConfig,
	applicationID,
	username,
	password,
	resource,
	callbacks...)

if (err == nil) {
    token := spt.Token
}
```

#### Authorization code authenticate

``` Go
spt, err := adal.NewServicePrincipalTokenFromAuthorizationCode(
	oauthConfig,
	applicationID,
	clientSecret,
      authorizationCode,
      redirectURI,
	resource,
	callbacks...)

err  = spt.Refresh()
if (err == nil) {
    token := spt.Token
}
```

### Command Line Tool

A command line tool is available in `cmd/adal.go` that can acquire a token for a given resource. It supports all flows mentioned above.

```
adal -h

Usage of ./adal:
  -applicationId string
        application id
  -certificatePath string
        path to pk12/PFC application certificate
  -mode string
        authentication mode (device, secret, cert, refresh) (default "device")
  -resource string
        resource for which the token is requested
  -secret string
        application secret
  -tenantId string
        tenant id
  -tokenCachePath string
        location of oath token cache (default "/home/cgc/.adal/accessToken.json")
```

Example acquire a token for `https://management.core.windows.net/` using device code flow:

```
adal -mode device \
    -applicationId "APPLICATION_ID" \
    -tenantId "TENANT_ID" \
    -resource https://management.core.windows.net/

```
