Hi,
Currently you cannot create Azure Cosmos DB custom role definitions via the portal. You could create them via PowerShell, for example:
$resourceGroupName = "MyCosmosDB-rg"
$accountName = "mycosmosdbaccount"
New-AzCosmosDBSqlRoleDefinition -AccountName $accountName `
-ResourceGroupName $resourceGroupName `
-Type CustomRole -RoleName CosmosReadMetadata `
-DataAction @( `
'Microsoft.DocumentDB/databaseAccounts/readMetadata') `
-AssignableScope "/"
Please see this FAQ:
Thanks.
-TP