* fix test failures.

* fixed mixer sha

Adds unary interfaces (related to envoyproxy/envoy-mobile#118) which will call into the streaming interfaces under the hood.

These are to be used as convenience convenience accessors for the common case of non-streaming requests, and will be added on Android as part of envoyproxy/envoy-mobile#119.

This also removes `data` and `trailers` from `Request`, as the unary function will take care of this for unary requests, and streams will be expected to handle this through the `StreamEmitter`.

The underlying implementation will look something like this:

```swift
public func sendUnary(_ request: Request, body: Data?,
                      trailers: [String: [String]] = [:], handler: ResponseHandler)
{
  let emitter = self.startStream(with: request, handler: handler)
  if let body = body {
    emitter.sendData(body)
  }

  emitter.close(trailers: trailers)
}
```

Signed-off-by: Michael Rebello <me@michaelrebello.com>
Signed-off-by: JP Simard <jp@jpsim.com>

Adds unary interfaces (related to envoyproxy/envoy-mobile#118) which will call into the streaming interfaces under the hood.

These are to be used as convenience convenience accessors for the common case of non-streaming requests, and will be added on Android as part of envoyproxy/envoy-mobile#119.

This also removes `data` and `trailers` from `Request`, as the unary function will take care of this for unary requests, and streams will be expected to handle this through the `StreamEmitter`.

The underlying implementation will look something like this:

```swift
public func sendUnary(_ request: Request, body: Data?,
                      trailers: [String: [String]] = [:], handler: ResponseHandler)
{
  let emitter = self.startStream(with: request, handler: handler)
  if let body = body {
    emitter.sendData(body)
  }

  emitter.close(trailers: trailers)
}
```

Signed-off-by: Michael Rebello <me@michaelrebello.com>
Signed-off-by: JP Simard <jp@jpsim.com>

Add support for setting cache size

Signed-off-by: LeiZhang <lei.a.zhang@intel.com>

**Commit Message**
Add authentication fields for accessing Azure OpenAI model.

**Related Issues/PRs (if applicable)**
Related PR: #347 

**Special notes for reviewers (if applicable)**
This is very first change to support Azure OpenAI model. I wanted to get
feedback on schema before proceed further changes. Please expect
subsequent PRs to support Azure OpenAI model integration.

---------

Signed-off-by: Xiaolin Lin <xlin158@bloomberg.net>

**Commit Message**

- Implement Azure OpenAI integration including a) backend auth handler
b) Azure token rotator.
- Replace oauth package with `token_provider` to simplify AWS and Azure
token request logic.
- Fix existing test case i.e. in backendsecurity_test.go when oidc is
nil for other provider.
- Centralize some of string literals in `constants.go`

**Related Issues/PRs (if applicable)**
Related Issue: #347 
Related PR: #424

---------

Signed-off-by: Xiaolin Lin <xlin158@bloomberg.net>
Signed-off-by: Dan Sun <dsun20@bloomberg.net>
Co-authored-by: Dan Sun <dsun20@bloomberg.net>