Autodesk ACC Forms access with two-legged OAuth Token

I'm attempting to use the ACC API to get the list of forms for a project but it fails with an HTTP 401 Unauthorized response that includes message "Authorization failed." This is while attempting to use a two-legged OAuth token, which I have successfully used for other ACC APIs, but the documentation indicates that a three-legged OAuth token is required for this particular endpoint. Using a three-legged token is not an option for the particular integration that I'm working on.

Has anyone else been able to use the Forms API with a two-legged OAuth token? For the APS support team that may see this, are there plans to support two-legged OAuth tokens for the ACC Forms API and when might that be implemented?

Unfortunately, ACC Forms API only supports three-legged access tokens right now, as documented.

However, we can use the SSA (Secure Service Account) API to provide a similar experience to the two-legged one, without requiring user logins.

• https://aps.autodesk.com/blog/update-secure-service-accounts-ssa-goes-ga
• https://aps.autodesk.com/blog/introducing-secure-service-accounts-ssa-now-public-beta
• https://github.com/autodesk-platform-services/aps-autodesk.ssa.api-postman.collection

Exchanging a three-legged access token using a self-signed JWT Assertion with the RSA private key we obtained during the creation of the SSA.

curl \
  --request POST \
  --url 'https://developer.api.autodesk.com/authentication/v2/token' \
  --header 'authorization: Basic xxx' \
  --header 'content-type: application/x-www-form-urlencoded' \
  --data 'grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer' \
  --data 'assertion=eyJraWQiOiI1ZGU5OTNmNC02MmIwLTQ5NWEtYTQzYS1iOTg5NmQ2ZTk1ODIiLCJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJKbE85VEExempmSlFPR1h....m6aLBKUTE1Htwpk0MUYmvl7AF03XDgWjhwRnJVOk_MkdF44bjSCAmsQ5uTYbWipUJjDqUy38b4xiRRRB0_qsg_kZ-DBOAFzUtYN6ilA'