How to temporarily give sysadmin to a user?

Below code is in a stored procedure and gives the following error when run under user: premfguser. Access to the remote server is denied because the current security context is not trusted.

SET @provider = 'Microsoft.Jet.OLEDB.4.0'
SET @ExcelString = 'Excel 8.0;Database=' + @fn

EXEC('INSERT INTO OPENROWSET(''' + @provider + ''',''' + @ExcelString + ''',''SELECT * FROM [Sheet1$A2开发者_JAVA技巧:L2]'') 
SELECT [ITEMNUMBER],'''',[ITEM_DESCRIPTION],[CASEPACK],[UNIT PRICE],[CASE PRICE],[WEIGHT],[CUBE],[CASE DIMS],[UPC],[CASE UPC],[Q Comments] FROM [ORDER SUMMERY] WHERE [Order #] = ''' + @OrderNumber + '''')

When I add premfguser to sysadmin it works. How can I run this code without permanently giving sysadmin to premfguser?

---

Use EXECUTE AS and sign the procedure with a certificate. See this example for how to sign a procedure, see also this article Signing Procedures with Certificates and this Tutorial: Signing Stored Procedures with a Certificate.

Note that the alternative of marking the database TRUSTWORTHY means that the dbo of the database is a de-facto sysadmin, as he can escalate himself to sysadmin anytime he likes if the trustworthy bit is set. Code signing is a much better alternative, although significantly more complex.

---

When you define the stored procedure, add the EXECUTE AS clause:

CREATE PROCEDURE SomeProcedure
WITH EXECUTE AS 'UserName'
AS BEGIN
  -- procedure code as usual...
END;