feat: add dynamic cors support

[poonai]

Signed-off-by: பாலாஜி balaji@dgraph.io

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[pawanrawal]

Mostly looking good, I'll approve. Just check and address the comments. Also, check with @gja about the behavior after DROP_ALL and DROP_DATA.

Reviewed 1 of 8 files at r1, 3 of 7 files at r2, 1 of 5 files at r4, 4 of 8 files at r6, 9 of 10 files at r7, 9 of 9 files at r8.
Reviewable status: all files reviewed, 9 unresolved discussions (waiting on @balajijinnah, @gja, @manishrjain, @MichaelJCompton, and @vvbalaji-dgraph)

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edgraph/server.go, line 89 at r8 (raw file):

	// AuthorizeCors is used to indicate that the given request is authorized to do
	// cors mutation.
	AuthorizeCors

CorsMutationAllowed

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edgraph/server.go, line 357 at r8 (raw file):

		// recreate the admin account after a drop data operation
		ResetAcl()
		ResetCors()

Should not be dropped on DROP_ALL and DROP_DATA

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edgraph/server.go, line 1224 at r8 (raw file):

}

func authorizeCors(ctx context.Context, qc *queryContext) error {

validateCorsInMutation

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edgraph/server.go, line 1621 at r8 (raw file):

	}
	corsRes := &corsResponse{}
	fmt.Println(string(res.Json))

remove this

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edgraph/server.go, line 1625 at r8 (raw file):

		return nil, err
	}
	//x.AssertTrue(len(corsRes.Me) == 1)

Print a glog.Error if len > 1

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graphql/admin/cors.go, line 86 at r8 (raw file):

// arrayToInterface convers array string to array interface
func arrayToInterface(in []string) []interface{} {

rather than doing this fix it in completeObject in graphql/resolve/resolver.go

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graphql/e2e/custom_logic/custom_logic_test.go, line 191 at r8 (raw file):

	result := params.ExecuteAsPost(t, alphaURL)
	if result.Errors != nil {

remove

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graphql/e2e/normal/normal_test.go, line 214 at r8 (raw file):

			"list": true,
			"index": true,
      		"tokenizer": [

formatting is messed up

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graphql/web/http.go, line 349 at r8 (raw file):

	w.Header().Set("Access-Control-Allow-Headers", x.AccessControlAllowedHeaders)
	w.Header().Set("Access-Control-Allow-Credentials", "true")
	w.Header().Set("Connection", "close")

this should be returned in all cases?

[gja]

I think it's best if DROP_DATA retains this data. If it's possible and not something that takes forever to implement.

Also, could we rename the methods too include the word origins?

getAllowedCORSOrigins / replaceAllowedCORSOrigins. Then the body can be {origins: []}

[manishrjain]

This PR introduced a bunch of issues in which Alpha server would not shut down correctly, @pawanrawal .