Rotating Databricks PAT for Power BI Gateway datasource via REST API (RSA-OAEP encrypted creds)

Context

1. I’m using a service principal that has:

• Power BI Admin role

• Gateway Admin on the target Enterprise Gateway

• Admin on the specific datasource/connection

• The necessary API permissions (per MS docs for Gateways/Datasources)

Docs I’m following: https://learn.microsoft.com/en-us/rest/api/power-bi/gateways/update-datasource#examples

1. We rotate PAT tokens in Databricks on a schedule and want to update the corresponding Power BI gateway datasource (non-VNet gateway) whenever the PAT changes.

2. I used the sample from the Microsoft “Encrypt credentials” repo to encrypt the payload with the gateway’s public key:
   https://github.com/microsoft/PowerBI-Developer-Samples/tree/master/Python/Encrypt%20credentials

Goal

Automate PATCH /gateways/{gatewayId}/datasources/{datasourceId} to update the Databricks PAT for an existing gateway datasource.

Wondering if i an get some help with REST API i get this error no matter what i try - "The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters. "

Sample payload 

 
"credentialDetails": {
"credentialType": "Key",
"credentials": "{\"credentialData\":[{\"name\":\"key\", \"value\":\"adad==\"}]}",
"encryptedConnection": "Encrypted",
"encryptionAlgorithm": "RSA-OAEP",
"privacyLevel": "None"
}