Fix context sql

[M4Al]

Why make this change?

• Fixes [Bug]: MSSQL (and related) - EXEC sp_set_session_context is executed with @read_only = 1 #2341 (partly)
  • do not set the session context in SQL server with read_only = 1 as this prevents us from doing a second request on the same connection
  • keep a copy of the original 'roles' from the JWT token so we can use it on the SQL Filter Predicate to accurately implement row level security

What is this change?

The changes itself are quite simple and should break nothing, see the diff :-)

How was this tested?

I have not created/adapted any tests yet. Just looking for comments before I go there.

Sample Request(s)

Sample of a JWT token (only the relevant part)
{ "aud": "api://ddcf6b31-5d01-407d-97cf-8efefc455d32", "iss": "https://sts.windows.net/9215c785-95c3-49b0-bdba-2062df5aedb5/", "roles": [ "user", "Allow_Customer_OPS025235", "Allow_Customer_OPS004095" ], "ver": "1.0" }

X-MS-API-ROLE: user

before my change the extra 'roles' that do not match the X-MS-API-ROLE header would never reach the database context.
With my change you can do things like this in SQL Predicates to filter out only subsets of the data:

`CREATE FUNCTION dbo.ops_fact_order_Predicate(@CustomerNo varchar(max))
RETURNS TABLE
WITH SCHEMABINDING
AS RETURN SELECT 1 AS fn_securitypredicate_result
WHERE @CustomerNo in (
select trim(replace(replace(replace([value], '"', ''), ']', ''), 'Allow_Customer_', ''))
from STRING_SPLIT (
CAST(SESSION_CONTEXT(N'original_roles') as varchar(max))
, ','
, 0)
where trim(replace(replace([value], '"', ''), ']', '')) like 'Allow_Customer%'
)

CREATE SECURITY POLICY dbo.ops_fact_order_Policy
ADD FILTER PREDICATE dbo.ops_fact_order_Predicate(CustomerNo)
ON [gold_ops].[ops_fact_order];`

[M4Al]

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