Connecting to OData

To connect to OData, you must set the Url to a valid OData service root URI. If your OData service does not have a root document, have FeedURL point to the specific entity you want to expose as a table.

You can also specify a CacheLocation to store the metadata of your OData organization. This keeps the CData ADO.NET Provider for OData from having to send requests for metadata on each connection.

Authenticating to OData

OData supports authentication via:

• HTTP
• Kerberos
• SharePoint Online
• OAuth
• Azure AD

HTTP Auth Schemes

For authenticating via HTTP, set AuthScheme according to the following table.

Scheme	AuthScheme	Other Settings
None	None	Use if no authentication is desired.
Basic	Basic	User, Password
NTLM (1)	NTLM	User, Password
Digest (if supported)	Digest	User, Password

(1) NTLM is a type of Windows authentication often used across a LAN using your Windows user credentials. Set the User and Password if you are not connecting from a Windows machine, or if your currently logged in user account should not be used for the connection.

Kerberos

To authenticate to OData using Kerberos, set these properties:

• hive.server2.authentication: Kerberos.
• AuthScheme: NEGOTIATE.
• KerberosKDC: The host name or IP Address of your Kerberos KDC machine.
• KerberosSPN: The service and host of the OData Kerberos Principal. Find this value just before the '@' symbol of the principal value.

SharePoint Online

SharePoint Online connections are established by retrieving a SharePoint Online cookie. To authenticate, set these properties:

• AuthScheme: SharePointOnline.
• User: The authenticating SharePoint Online user account.
• Password: The authenticating account's password.

OAuth

To enable this authentication from all OAuth flows in OData, you must create a custom OAuth application, and set AuthScheme to OAuth.

The following subsections describe how to authenticate to OData from three common authentication flows. For information about how to create a custom OAuth application, see Creating a Custom OAuth Application. For a complete list of connection string properties available in OData, see Connection.

Desktop Applications

To authenticate with the credentials for a custom OAuth application, you must get and refresh the OAuth access token. After you do that, you are ready to connect.

Set these properties:

• InitiateOAuth: GETANDREFRESH. Used to automatically get and refresh the OAuthAccessToken.
• OAuthClientId: The client Id assigned when you registered your custom OAuth application.
• OAuthClientSecret: The client secret that was assigned when you registered your custom OAuth application.
• CallbackURL: The redirect URI that was defined when you registered your custom OAuth application.

When you connect, the provider opens OData's OAuth endpoint in your default browser. Log in and grant permissions to the application.

After you grant permissions to the application, the provider completes the OAuth process:

1. The provider obtains an access token from OData and uses it to request data.
2. The OAuth values are saved in the path specified in OAuthSettingsLocation. These values persist across connections.

When the access token expires, the provider refreshes it automatically.

Web Applications

Authenticating via the Web requires you to create and register a custom OAuth application with OData, as described in Creating a Custom OAuth Application. You can then use the provider to get and manage the OAuth token values.

This section describes how to get the OAuth access token, how to have the driver refresh the OAuth access token automatically, and how to refresh the OAuth access token manually.

Get the OAuth access token:

1. To obtain the OAuthAccessToken, set these connection properties :
   • OAuthClientId: The client Id in your custom OAuth application settings.
   • OAuthClientSecret: The client secret in your custom OAuth application settings.

2. Call stored procedures to complete the OAuth exchange:
   • Call the GetOAuthAuthorizationUrl stored procedure. Set the AuthMode input to WEB and the CallbackURL to the Redirect URI you specified in your custom OAuth application settings. The stored procedure returns the URL to the OAuth endpoint.
   • Navigate to the URL that the stored procedure returned in Step 1. Log in and authorize the web application. You are redirected back to the callback URL.
   • Call the GetOAuthAccessToken stored procedure. Set the AuthMode input to WEB. Set the Verifier input to the code parameter in the query string of the redirect URI.

After you obtain the access and refresh tokens, you can connect to data and refresh the OAuth access token automatically.

Automatic refresh of the OAuth access token:

To have the provider automatically refresh the OAuth access token:

1. Before connecting to data for the first time, set these connection parameters:
   • InitiateOAuth: REFRESH.
   • OAuthClientId: The client Id in your custom OAuth application settings.
   • OAuthClientSecret: The client secret in your custom OAuth application settings.
   • OAuthAccessToken: The access token returned by GetOAuthAccessToken.
   • OAuthSettingsLocation: The path where you want the provider to save the OAuth values, which persist across connections.
2. On subsequent data connections, set:
   • InitiateOAuth
   • OAuthSettingsLocation

Manual refresh of the OAuth access token:

The only value needed to manually refresh the OAuth access token is the OAuth refresh token.

1. To manually refresh the OAuthAccessToken after the ExpiresIn period (returned by GetOAuthAccessToken) has elapsed, call the RefreshOAuthAccessToken stored procedure.
2. Set these connection properties:
   • OAuthClientId: The Client Id in your custom OAuth application settings.
   • OAuthClientSecret: The Client Secret in your custom OAuth application settings.

3. Call RefreshOAuthAccessToken with OAuthRefreshToken set to the OAuth refresh token returned by GetOAuthAccessToken.
4. After the new tokens have been retrieved, set the OAuthAccessToken property to the value returned by RefreshOAuthAccessToken. This opens a new connection.

Store the OAuth refresh token so that you can use it to manually refresh the OAuth access token after it has expired.

Headless Machines

If you need to log in to a resource that resides on a headless machine, you must authenticate on another device that has an internet browser. You can do this in either of the following ways:

• Option 1: Obtain the OAuthVerifier value.
• Option 2: Install the provider on a machine with an internet browser and transfer the OAuth authentication values after you authenticate through the usual browser-based flow.

After you execute either Option 1 or Option 2, configure the driver to automatically refresh the access token on the headless machine.

Option 1: Obtaining and Exchanging a Verifier Code

To obtain a verifier code, you must authenticate at the OAuth authorization URL as follows:

1. Authenticate from the machine with an internet browser, and obtain the OAuthVerifier connection property.

   Set these properties:

   • InitiateOAuth: OFF.
   • OAuthClientId: The client Id assigned when you registered your custom OAuth application.
   • OAuthClientSecret: The client secret assigned when you registered your custom OAuth application.

2. Call the GetOAuthAuthorizationUrl stored procedure. The stored procedure returns the CallbackURL established when the custom OAuth application was registered. (See Creating a Custom OAuth Application.)

   Copy this URL and paste it into a new browser tab.

3. Log in and grant permissions to the provider. The OAuth application redirects you the redirect URI, with a parameter called code appended. Note the value of this parameter; you will need it later, to configure the OAuthVerifier connection property.

4. Exchange the OAuth verifier code for OAuth refresh and access tokens. On the headless machine, to obtain the OAuth authentication values, set these properties:

   • InitiateOAuth: REFRESH.
   • OAuthVerifier: The noted verifier code (the value of the code parameter in the redirect URI).
   • OAuthSettingsLocation: Persist the encrypted OAuth authentication values to the specified file.
   • OAuthClientId: The client Id in your custom OAuth application settings.
   • OAuthClientSecret: The client secret in the custom OAuth application settings.

5. Test the connection to generate the OAuth settings file.

6. You are ready to connect after you re-set these properties:

   • InitiateOAuth: REFRESH.
   • OAuthSettingsLocation: The file containing the encrypted OAuth authentication values. To enable the automatic refreshing of the access token, be sure that this file gives read and write permissions to the provider.
   • OAuthClientId: The client Id assigned when you registered your custom OAuth application.
   • OAuthClientSecret: The client secret assigned when you registered your custom OAuth application.

Option 2: Transferring OAuth Settings

Prior to connecting on a headless machine, you must install and create a connection with the driver on a device that supports an internet browser. Set the connection properties as described above in "Desktop Applications".

After completing the instructions in "Desktop Applications", the resulting authentication values are encrypted and written to the path specified by OAuthSettingsLocation. The default filename is OAuthSettings.txt.

Test the connection to generate the OAuth settings file, then copy the OAuth settings file to your headless machine.

To connect to data via the headless machine, set these connection properties:

• InitiateOAuth: REFRESH
• OAuthSettingsLocation: The path to the OAuth settings file you copied from the machine with the browser. To enable automatic refreshing of the access token, ensure that this file gives read and write permissions to the provider.
• OAuthClientId: The client Id assigned when you registered your custom OAuth application.
• OAuthClientSecret: The client secret assigned when you registered your custom OAuth application.

Azure AD

Azure AD supports a form of OAuth that goes through Azure. Set the AuthScheme to AzureAD.

The CData ADO.NET Provider for OData automatically takes care of known Azure URLs internally, so it is not necessary to specify any of the usual OAuth connection properties, such as OAuthAccessTokenURL, OAuthAuthorizationURL,OAuthRefreshTokenURL, and OAuthRequestTokenURL.

Other connection properties may be required for this connection method including:

• Scope: Must be specified if InitiateOAuth is set to GETANDREFRESH as the Scope is submitted to Microsoft during retrieval of credentials. This varies depending on the service, but is generally a combination of the resource (hostname in the URL) and permission name. For example: https://host/user_impersonation.
• AzureADResource: The specific Azure Resource to authenticate against during Microsoft login. If none is specified, your user account's default resource is used.
• AzureADTenant: The specific Azure Tenant to authenticate against during Microsoft login. If none is specified, your user account's default tenant via the common login endpoint is used. This may not be correct depending on the specific resource you are connecting to, or if the resource is stored on a seperate tenant.

Otherwise, the steps to authenticate are identical to the descriptions of Desktop, Web, and Headless Machine authentication.

For information about how to create a custom OAuth application for use with Azure AD, see Creating a Custom OAuth Application.

Securing OData Connections

By default, the provider attempts to negotiate SSL/TLS by checking the server's certificate against the system's trusted certificate store. To specify another certificate, see the SSLServerCert property for the available formats to do so.