Is it considered acceptable/safe to use an Azure AD access token in the browser for Cognitive Services when /issueToken is unavailable?

Question

Is it considered acceptable/safe to use an Azure AD access token in the browser for Cognitive Services when /issueToken is unavailable?

Brett Jewell 20

I am currently using the /issueToken endpoint to obtain a short-lived token, which I then pass to the frontend browser client for use with the Speech SDK.

I am migrating to a Speech resource configured with a private endpoint, which means the /issueToken endpoint is no longer available.

My plan is to use the Microsoft Entra (Azure AD) authentication flow to acquire an Azure AD access token.

Is it considered acceptable and safe to pass this Azure AD token directly to a frontend browser client for use with the Speech SDK? If not, what are the recommended alternatives or best practices in this scenario?

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Anonymous

2025-11-19T18:18:05.37+00:00

Hi Brett Jewell

Did you get any chance to review the above response. Thank you!
Brett Jewell 20 Reputation points

2025-11-19T18:30:26.0366667+00:00

Hi, thanks for the response. Could you clarify option 1 — specifically the part about “exchanging the token for a short-lived Speech service token”? I haven’t seen any documentation or examples showing that this kind of token exchange is supported for Speech.

My understanding is that there isn’t a way to obtain a short-lived client-safe token from the browser’s Azure AD token. And since you confirmed that using the Azure AD token directly isn’t recommended, it seems like option 2 is the path I’ll need to take.
Anonymous

2025-11-19T19:41:11.6833333+00:00

Hi Brett Jewell

Azure Speech doesn’t currently support a direct token exchange mechanism where you take an Azure AD token and convert it into a short-lived Speech-specific token. The /issueToken endpoint is the only supported way to obtain a client-safe token for browser use, and that endpoint itself requires an API key.

So, to clarify:

Option 1 (Token Exchange)

This is not available for Speech. There’s no documented flow to exchange an Azure AD token for a Speech service token.

The Speech SDK expects either:

An API key, or

A short-lived token obtained from /issueToken (which itself requires an API key).

Option 2 (Recommended Approach)

Implement a server-side token broker:

Your backend uses the Speech resource API key to call /issueToken.

It returns the short-lived token (valid for ~10 minutes) to the browser.

The browser uses this token with the Speech SDK for secure calls.

This pattern ensures:

API keys stay on the server.

The browser only handles short-lived tokens, reducing exposure risk.
Brett Jewell 20 Reputation points

2025-11-19T19:51:27.1066667+00:00

Thanks for confirming. To come full circle: /issueToken is disabled when ‘All networks access’ isn’t enabled, which is the case for my setup. So instead, I’ll need to use the Speech SDK on the backend and forward the responses to the client.
Anonymous

2025-11-19T19:54:55.4033333+00:00

Hi Brett Jewell

when “All networks access” is disabled, the /issueToken endpoint becomes unavailable because it relies on public network access. In that scenario, the safest and most practical approach is exactly what you described:

Backend Speech SDK Flow

Client sends audio or text to your backend over a secure channel (HTTPS).

Backend uses Speech SDK or REST API with the resource’s API key to perform:

Speech-to-Text (STT)

Text-to-Speech (TTS)

Translation, etc.

Backend returns the processed result (e.g., recognized text or audio stream) to the client.

Answer 1

Hi Brett Jewell

Welcome to Microsoft Q&A,

Passing an Azure AD access token directly to a browser client for Cognitive Services (e.g., Speech SDK) is not recommended for security reasons. Here’s why and what you should do instead:
It’s Risky

Exposure of a powerful token: An Azure AD access token typically grants broad permissions tied to the user or app identity. If leaked (e.g., via browser dev tools, logs, or XSS), it could be misused to access other Azure resources.
Longer lifetime than /issueToken: Unlike the short-lived token from /issueToken (usually ~10 minutes), Azure AD tokens often last 1 hour or more, increasing the attack window.
No resource scoping: The token might allow access beyond Speech services unless you strictly scope it to the Speech resource.

Recommended Alternatives

Use a Backend Token Broker
- Implement a secure server-side component that:
- Authenticates with Azure AD.
- Exchanges the token for a short-lived Speech service token (or signs requests if using private endpoints).
- Returns only the minimal token to the browser.
- This mimics /issueToken behavior and keeps sensitive credentials off the client.
Enable Managed Identity or Service Principal
- For private endpoints, authenticate your backend using a managed identity or service principal.
- The backend then calls Speech service and streams audio results to the client (instead of exposing tokens).
If Direct Token Use Is Unavoidable
- Scope the token: Request an access token for the Speech resource only (https://cognitiveservices.azure.com/.default).
- Use HTTPS and secure storage: Never store tokens in localStorage; keep them in memory.
- Shorten lifetime: Use conditional access or token lifetime policies to minimize exposure.

Notes:

Never expose long-lived or broadly scoped tokens to the browser.
Always prefer a backend proxy pattern for private endpoints.
If you must use Azure AD tokens in the browser, apply strict scoping and lifetime controls.

I Hope this helps. Do let me know if you have any further queries.

Thank you!

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Is it considered acceptable/safe to use an Azure AD access token in the browser for Cognitive Services when /issueToken is unavailable?

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