Introduce JWT Flow API in Test Support

[jzheaux]

It would be handy in tests to be able to specify a Jwt authentication in tests:

this.mockMvc.perform(get("/")
        .with(jwt()))
        .andExcept(status().isOk());

Some features we should consider:

• Providing a completely instantiated Jwt:

Jwt jwt = ...;
this.mockMvc.perform(get("/")
        .with(jwt(jwt)))
        ...

• Providing authorities:

Jwt jwt = ...;
this.mockMvc.perform(get("/")
        .with(jwt(jwt).authorities("SCOPE_message:read"))
        ...

• Providing claims:

this.mockMvc.perform(get("/")
        .with(jwt().claim(SUB, "the-subject")))
        ...

• Providing headers:

this.mockMvc.perform(get("/")
        .with(jwt().header("alg", RS256)))
        ...

These would result in the SecurityContext containing an instance of JwtAuthenticationToken.

Also, we should introduce its reactive equivalent.

[ch4mpy]

Using mockJwt() instead of jwt() to be consistent with existing mockUser(). It also make things consistent with annotations: with(mockJwt()) <=> @WithMockJwt

Missed the part of the spec with the Jwt instance. Will fix that soon.

Went further this spec as I propose equivalents for Bearer access-token and OidcId token.

All is based on commons I initiated for annotations equivalents (#6557)

Branches are ordered as follow (so PRs are streamed as follow):

1. gh-6634--jwt-servlet-flow mockJwt() flow API for MockMvc
2. gh-6634--access-token-servlet-flow mockAccessToken() flow API for MockMvc
3. gh-6634--oidcid-servlet-flow mockOidcId() flow API for MockMvc
4. gh-6557--jwt-reactive-flow mockJwt() flow API for reactive server
5. gh-6557--access-token-reactive-flow augment reactive flow with mockOidcId()
6. gh-6557--oidcid-reactive-flow mockOidcId() flow API for reactive server